There’s a quick way you can enable or disable this annoying window from the command line:

Disable UAC

reg.exe ADD HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System /v EnableLUA /t REG_DWORD /d 0 /f

Enable UAC

reg.exe ADD HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System /v EnableLUA /t REG_DWORD /d 1 /f

After you enable or disable UAC, you will have to reboot your computer for the changes to take effect.