Windows (7|10) Registry Mods

Negotiating the labyrinth.

Keys affecting File Type Association (FTA) and other useful mods

Change a filetype's icon, reported type, and handler(s), and/or add a (custom) app to File Explorer's context menu. The relevant registry keys, and two CLI-based methods for modifying them, are detailed herein. One method involves exporting, modifying, and then adding back .reg files. The other method is entirely programmatic. Both allow for scripting to batch process any list of such mods.

Some (protected) file types require a two-step process to modify their FTA app or icon; first delete the key, then add it back. This is due to restrictions written into a type's subkey(s). Examples of such are detailed below.
If changes aren't immediately apparent after modifications, then toggle the targeted type's handler, e.g., to Notepad and then back, per "Open with"->"Always use ...", and/or refresh Windows icon cache per ie4uinit.exe -show.

Lots of mystery, paranoia, and misinformation surround the Windows registry. Having worked with it quite a bit over the decades, experience indicates that any target key(s) should first be exported and archived, unaltered, as can be the entire registry. Keys can then be restored simply and reliably, unless the damage is too extensive. Again from experience, just about the only way to truly screw things up beyond the target key is to programmatically insert a malformed key or entry. That is, to inject improper syntax. Even then, it takes a very unfortunate mix of such syntax to harm the registry irreparably, or otherwise even affect it beyond the target key. The registry is not fragile.

FTA entries

Most reside at subkeys of HKEY_CLASSES_ROOT (HKCR)

`HKCR\.{TYPE}`

Modify only by pointing to a (created) key where the FTA mods reside. A standard naming convention used by applications for their FTAs is HKCR\{APP}.{TYPE} or HKCR\{APP}{TYPE}. Absent any such app, the naming convention is HKCR\{TYPE}file or HKCR\{TYPE}_auto_file. All such keys are equivalents; they're for FTA settings, as detailed later. This key should point to the one desired. E.g., ...
```
[HKEY_CLASSES_ROOT\.{TYPE}]
@="{TYPE}file"
```
Two entry values prevent certain other filetype mods. Delete them as necessary, if they exist.
```
[HKEY_CLASSES_ROOT\.{TYPE}]
@="{TYPE}"
"EditFlags"=dword:002...
"FriendlyTypeName"="@C:\\...\\ieframe.dll,-914"
```
- "EditFlags"=-
- "FriendlyTypeName"=-
These entries may also exist at other registry keys regarding the filetype, e.g., at subkeys under the HKCU hive (HKCU\SOFTWARE\...\Explorer\FileExts\.{TYPE}). Such keys regenerate any required subkey per user-select actions, and so may be deleted entirely, as discussed later.
Add {TYPE} filetype to the New file (creation) list @ File Explorer's context menu, along with an optional template file:
```
[HKEY_CLASSES_ROOT\.{TYPE}\ShellNew]
"NullFile"=""
"FileName"="C:\\path to\\optional template file\\New.{TYPE}"
```
This optional New list mod is orthogonal to FTA mod(s). It's a very useful mod, spawining the custom per-type template file anew in the current folder with a single click.

`HKCR\{TYPE}file`

This is where most FTA customizations should reside. Mods in this hive (HKCR) persist, survive, and recover from subsequent user-select FTA actions, unlike those in the HKCU hive. Be sure the primary file-type key, HKCR\.{TYPE}, is modified to point to this key, whatever this key is actually named. (See naming convention discussed above.)
```
[HKEY_CLASSES_ROOT\{TYPE}file]
@="{TYPE}"
"Content Type"="text/{TYPE}"
"PerceivedType"="text"
```
Here only, at the @="{TYPE}" entry, {TYPE} can be any string; it's the term for the file type reported by File Explorer, not a key-name reference as is that same entry under the HKCR\.{TYPE} key. Confusions abound!
Create "NeverShowExt"="" entry, optionally, to hide the extension of {TYPE} regardless of settings at
File Explorer GUI. The entry is typically inserted here, though elsewhere for certain cases.
```
[HKEY_CLASSES_ROOT\{TYPE}file]
 "NeverShowExt"=""
```
NeverShowExt mod is only worth the trouble if in developer mode, whereof the File Explorer GUI setting is display known file extensions, which applies to all types. This method overrides that setting per target type, affecting no others.

Set DefaultIcon to the desired (custom) icon (path):

[HKEY_CLASSES_ROOT\{TYPE}file\DefaultIcon]
@="C:\\ICONS\\{TYPE}.ico,0"

Add FTA app(s) to File Explorer's context menu, as handlers
for Open, Edit, Run, ... actions per {TYPE} filetype.

[HKEY_CLASSES_ROOT\{TYPE}file\shell]

[HKEY_CLASSES_ROOT\{TYPE}file\shell\edit]

[HKEY_CLASSES_ROOT\{TYPE}file\shell\edit\command]
@="\"C:\\Program Files\\Microsoft VS Code\\Code.exe\" \"%1\""

[HKEY_CLASSES_ROOT\{TYPE}file\shell\open]

[HKEY_CLASSES_ROOT\{TYPE}file\shell\open\command]
; This would run the file and any args directly, e.g., '.bat' type
@="\"%1\" %*"

[HKEY_CLASSES_ROOT\{TYPE}\shell\run]
@="Process per typeProcessor"
"Icon"="S:\\path to\\the app\\typeProcessor.exe,0"

[HKEY_CLASSES_ROOT\{TYPE}\shell\run\command]
@="\"S:\\path to\\the app\\typeProcessor.exe\" \"%1\""

Entries in this hive (HKCR) are not overwritten by subsequent user actions, unlike those at HKCU. That is, though FTAs (app/icon) are hijacked upon any subsequent "Open with"->"Always use ..." user-select action (UserChoice), they do restore whenever that selection is back to the app designated herein. Contrarily, mods @ HKCU never restore, since they are overwritten upon any user-select. (See HKCU\...\.{TYPE}\UserChoice section.)

Again, this subkey name, {TYPE}file, is just an example. Such keys may be auto-generated by some related app, per install or other process; or created by us. As mentioned in the section on the primary file-type key, HKCR\.{TYPE}, the standard naming convention for this FTA key, used by applications for their FTAs, is HKCR\{APP}.{TYPE} or HKCR\{APP}{TYPE}. And absent any such app, the naming convention is HKCR\{TYPE}file or HKCR\{TYPE}_auto_file. All such keys are equivalents; they're for these FTA settings. Just make sure the primary key points to the one containing the desired mods, whatever its name. It's okay for several such keys to exist for a given file-type, even though only one is used.

`HKCR\Applications\{APPNAME}`

Add an (unregistered) app to File Explorer's Context Menu. Use only when not an FTA app; otherwise, use the method shown above, at a HKCR\{TYPE}file\shell sub-key.

[HKEY_CLASSES_ROOT\Applications\{APP}.exe]

[HKEY_CLASSES_ROOT\Applications\{APP}.exe\DefaultIcon]
@="S:\\path to\\the app\\{APP}.exe,0"

[HKEY_CLASSES_ROOT\Applications\{APP}.exe\shell]

[HKEY_CLASSES_ROOT\Applications\{APP}.exe\shell\run]

[HKEY_CLASSES_ROOT\Applications\{APP}.exe\shell\run\command]
@="\"S:\\path to\\the app\\{APP}.exe\" \"%1\""

`HKCU\SOFTWARE\...\Explorer\FileExts\.{TYPE}`

This key has 3 subkeys, OpenWithList, OpenWithProgids, and UserChoice. They can all be deleted and then, for good measure, recreated sans entries. They automatically regenerate/repopulate on any subsequent user-select.

UserChoice sets the FTA; the one system-wide app associated with the filetype.
Delete the ProgId entry. Okay to also (re)set it, but that is usually unnecessary.

[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.{TYPE}\UserChoice]
"ProgId"="{TYPE}file"

Special cases, such as url and html ...

[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.html\UserChoice]
"ProgId"="FirefoxHTML-308046B0AF4A39CB"

UserChoice is where FTA and icon settings are hijacked per app. The subkey is overwritten per subsequent user-select (UserChoice) actions, "Open with"->"Always use ...", unlike setting(s) at the HKCR\{TYPE}file key. Comparing mods at the two hives, HKCR vs. HKCU, while the immediate effects from any user-select actions are the same, the big difference is that HKCR settings recover (FTA & icon) upon user-select back to whatever handlers were programmed therein. Whereas any mods here (HKCU\...\UserChoice) are gone, having been overwritten. This is the cause of much user unhappiness.

`HKCR\Directory`

Add (non-FTA) apps to File Explorer's context menu.
Example:

[HKEY_CLASSES_ROOT\Directory\Background\shell\CyghereAdmin]
@="Cygwin Admin Here"
"Icon"="C:\\Cygwin\\Cygwin-Terminal.ico,0"

[HKEY_CLASSES_ROOT\Directory\Background\shell\CyghereAdmin\command]
@=":\\cygwin\\bin\\minttyAdmin.exe -i /Cygwin-Terminal.ico -e /bin/xhere /bin/bash.exe"
; This method requires Cygwin's 'chere' package.

Such mods, in the HKCR\Directory subkey, are orthogonal to FTA.

Programmatically Add/Modify/Delete Registry Keys

Two methods, using Windows native command-line tools
- regedit.exe /s|/e FILE.reg
- reg.exe add|delete KEYpath

`regedit /s FILE.reg` method.

Simple, quick, and quite legible:
- Export the target (sub)key to a .reg file:
  regedit /e "HKCR.foo.reg" "HKCR\.foo".
- Edit the file, and then load (merge) it back:
  regedit /s "HKCR.foo.reg".
Can be made as programmatic as the other method by having some orthogonal process auto-generate the FILE.reg.

Delete

regedit /s FILE.reg

Delete (sub)keys by prepending a hyphen, -, e.g., [-HKEY...]
Delete entries by appending a hyphen, -, e.g., "Entry"=-

At times when the reg delete KEYpath /f method fails per DENIED: ..., this method succeeds.

Add

regedit /s FILE.reg

Merges the data. Same as double-click on the file, sans query/report GUI. That is, it does NOT remove keys/vals which do not exist in FILE.reg. So, manual or programmatic deletion is required for such effect. Likewise, before (re)loading a (modified) key, remove all irrelevant keys from the file. If not, it increases the chances of the key merge (partially) failing due to some active process(es) involving those irrelvant subkeys.

`reg add|delete KEYpath` method.

Accepts abbreviations for the four main hive key-names:

HKEY_LOCAL_MACHINE      HKLM
HKEY_CURRENT_USER       HKCU
HKEY_USERS              HKU
HKEY_CURRENT_CONFIG     HKCC

reg query|save ... are also useful here.

Delete

reg delete ROOTKEY\SubKey /f 

    ROOTKEY  [ HKLM | HKCU | HKCR | HKU | HKCC ]

    /va        delete all values under this key.

    /f         Forces the deletion without prompt.

E.g., delete the key and all subkeys thereunder:

reg delete HKCR\foofile /f

Add

reg add ROOTKEY\SubKey ...

    ROOTKEY  [ HKLM | HKCU | HKCR | HKU | HKCC ]

    /v       The value name, under the selected Key, to add.

    /ve      adds an empty value name (Default) for the key

    /t       RegKey data types (defaults to REG_SZ)
             [ REG_SZ  | REG_MULTI_SZ | REG_EXPAND_SZ |
             REG_DWORD | REG_QWORD    | REG_BINARY    | REG_NONE ]

    /d       The data to assign to the registry ValueName being added.

    /f       Force overwriting the existing registry entry without prompt.

Examples

Add default (custom) icon for filetype `foo`:

reg add HKCR\foofile\DefaultIcon /ve /d "C:\ICONS\foo.ico"

Creates a default (REG_SZ) data-type value at an "empty value name", @=..., entry:

[HKEY_CLASSES_ROOT\foofile\DefaultIcon]  
@="C:\\ICONS\\foo.ico"

Add the `NeverShowExt` value (flag) for filetype `foo`:

reg add HKCR\foofile /v "NeverShowExt"

Creates a value name having an empty string value of default (REG_SZ) data type:

[HKEY_CLASSES_ROOT\foofile]  
"NeverShowExt"=""

Add `foo` filetype and its template file, `New.foo`, to File Explorer's `New` menu:

reg add HKCR\.foo\ShellNew /v "FileName" /d "C:\ICONS\ShellNew\New.foo"
reg add HKCR\.foo\ShellNew /v "Nullfile"

Creates:

[HKEY_CLASSES_ROOT\.foo\ShellNew]
"FileName"="C:\\ICONS\\ShellNew\\New.foo"
"Nullfile"=""

`FTA`; associate filetype `foo` with its `edit` handler (app):

reg add HKCR\foofile\shell\edit\command /ve /t REG_EXPAND_SZ   
/d "\"C:\\Program Files\\Microsoft VS Code\\Code.exe\" \"^%1\""

Creates a REG_EXPAND_SZ data type:

[HKEY_CLASSES_ROOT\foofile\shell\edit\command]  
@=hex(2):22,00,43,00,3a,00,5c,00,5c,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,\  
00,20,00,46,00,69,00,6c,00,65,00,73,00,5c,00,5c,00,4d,00,69,00,63,00,72,00,\  
6f,00,73,00,6f,00,66,00,74,00,20,00,56,00,53,00,20,00,43,00,6f,00,64,00,65,\  
00,5c,00,5c,00,43,00,6f,00,64,00,65,00,2e,00,65,00,78,00,65,00,22,00,20,00,\  
22,00,25,00,31,00,22,00,00,00

`FTA`, same as above, using the default data-type:

reg add HKCR\foofile\shell\edit\command /ve   
/d "\"C:\Program Files\Microsoft VS Code\Code.exe\" \"^%1\"" /f

Creates:

[HKEY_CLASSES_ROOT\foofile\shell\edit\command]  
@="\"C:\\Program Files\\Microsoft VS Code\\Code.exe\" \"%1\""

`FTA.Add.cmd` (example script)

@echo off
:: -------------------------------------------------------
::  REG ADD :: FTA for filetype %1
::  
::  - Requires app path (hardcoded here) 
:: -------------------------------------------------------

::set _prog=C:\Program Files\7-Zip\7zFM.exe
::set _icons=C:\ICONS\archs
set _prog=C:\Program Files\Microsoft VS Code\Code.exe
set _icons=C:\ICONS
set _ext=%~1
if not exist "%_prog%" ( echo. & echo   ABORTed :: App does NOT EXIST & echo. & pause & goto :eof )
if not exist "%_icons%" ( echo. & echo   ABORTed :: '%_icons%' folder does NOT EXIST & echo. & pause & goto :eof )
if "%_ext%" == "" ( echo. & echo   ABORTed :: filetype name [extension name] REQUIREd & echo. & pause & goto :eof )
echo. & echo   REG ADD :: Set FTA and such for filetype '%_ext%' & echo. & pause & echo. 

:: ==  HKCR  ==

echo DEL+ADD @ HKCR\.%_ext% 
reg delete HKCR\.%_ext% /f
reg add HKCR\.%_ext% /ve /d "%_ext%file"

echo DEL+ADD @ HKCR\%_ext%file
reg delete HKCR\%_ext%file /f
reg add HKCR\%_ext%file /ve /d "%_ext%"
reg add HKCR\%_ext%file /v "NeverShowExt"
reg add HKCR\%_ext%file\DefaultIcon /ve /d "%_icons%\%_ext%.ico,0"

:: no app yet associated with filetype, so "Open with ..." (Always) selection allows
:: user-selected app to PERMANENTLY steal/replace the icon. So need to specify app here:
echo DEL+ADD @ HKCR\%_ext%file\shell
reg delete HKCR\%_ext%file\shell /f
reg add HKCR\%_ext%file\shell\open\command /ve /d "\"%_prog%\" \"^%%1\"" 

:: ==  HKCU  ==

echo DEL @ HKCU\...\FileExts\.%_ext% 
:: Windows overwrites this key per user's "Open with ..." (Always) selection
:: That's how icon setting is hijacked per app, 
:: so UNSET (DELETE) ONLY. Can set it, but don't have to (usually).
:: Deletion DENIED if associated with , e.g., Notepad.exe ; if so, use reg key method, [-HKEY....], instead.
::reg delete HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext% /f
>  "%TEMP%\HKCU.%_ext%.reg" echo Windows Registry Editor Version 5.00
>> "%TEMP%\HKCU.%_ext%.reg" echo. 
>> "%TEMP%\HKCU.%_ext%.reg" echo [-HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%]
regedit /s "%TEMP%\HKCU.%_ext%.reg"

echo ADD empties @ HKCU\...\FileExts\.%_ext%\... +OpenWithList +OpenWithProgids +UserChoice
:: Add back empty keys
>  "%TEMP%\HKCU.%_ext%.reg" echo Windows Registry Editor Version 5.00
>> "%TEMP%\HKCU.%_ext%.reg" echo. 
>> "%TEMP%\HKCU.%_ext%.reg" echo [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%]
>> "%TEMP%\HKCU.%_ext%.reg" echo. 
>> "%TEMP%\HKCU.%_ext%.reg" echo [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%\OpenWithList]
>> "%TEMP%\HKCU.%_ext%.reg" echo. 
>> "%TEMP%\HKCU.%_ext%.reg" echo [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%\OpenWithProgids]
>> "%TEMP%\HKCU.%_ext%.reg" echo. 
>> "%TEMP%\HKCU.%_ext%.reg" echo [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%\UserChoice]
regedit /s "%TEMP%\HKCU.%_ext%.reg"

:: 'HKCU\...\OpenWithList' not needed
::echo ADD @ HKCU\...\FileExts\.%_ext%\OpenWithList 
::reg add HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%\OpenWithList /ve /t REG_SZ 

:: 'HKCU\...\OpenWithProgids' not needed
::echo ADD @ HKCU\...\FileExts\.%_ext%\OpenWithProgids 
::reg add HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%\OpenWithProgids /v "%_ext%file" /t REG_NONE

:: 'HKCU\...\UserChoice' not needed (usually)
:: Windows overwrites this key per user's "Open with ..." (Always) selection
::echo ADD @ HKCU\...\FileExts\.%_ext%\UserChoice 
::reg add HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.%_ext%\UserChoice /v "ProgId" /d "%_ext%file" 


echo. & echo   DONE & echo. & pause
goto :eof
*********

Windows (7|10) Registry Mods

Keys affecting File Type Association (FTA) and other useful mods

FTA entries

HKCR\.{TYPE}

HKCR\{TYPE}file

HKCR\Applications\{APPNAME}

HKCU\SOFTWARE\...\Explorer\FileExts\.{TYPE}

HKCR\Directory

Programmatically Add/Modify/Delete Registry Keys

regedit /s FILE.reg method.

Delete

Add

reg add|delete KEYpath method.

Delete

Add

Examples

Add default (custom) icon for filetype foo:

Add the NeverShowExt value (flag) for filetype foo:

Add foo filetype and its template file, New.foo, to File Explorer's New menu:

FTA; associate filetype foo with its edit handler (app):

FTA, same as above, using the default data-type:

FTA.Add.cmd (example script)

`HKCR\.{TYPE}`

`HKCR\{TYPE}file`

`HKCR\Applications\{APPNAME}`

`HKCU\SOFTWARE\...\Explorer\FileExts\.{TYPE}`

`HKCR\Directory`

`regedit /s FILE.reg` method.

`reg add|delete KEYpath` method.

Add default (custom) icon for filetype `foo`:

Add the `NeverShowExt` value (flag) for filetype `foo`:

Add `foo` filetype and its template file, `New.foo`, to File Explorer's `New` menu:

`FTA`; associate filetype `foo` with its `edit` handler (app):

`FTA`, same as above, using the default data-type:

`FTA.Add.cmd` (example script)