Windows 7 file extension association

Question

I am referring specifically to windows 7.

I have code that associates a certain extension with my application as proposed by webJose on the following page: What registry

Answer 1

Also on Windows 10, this command can't work:

Reg.exe delete "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.m4v" /f

The solution is to delete the SID key by running a BAT file under TrustedInstaller (with NSudo, PowerRun, etc):

for /f "delims=\ tokens=2" %%A in ('reg query hku ^| findstr /i "S-1-5-21-" ^| findstr /v /i "_Classes"') do set SID=%%A
Reg.exe delete "HKU\%SID%\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.m4v" /f

P.S.: Thanks to @SecurityAndPrivacyGuru for sharing the SID detection command.