Not sure if you REQUIRE the setting to come from local group policy, but if you want to bypass the group policy problems, just set this Registry Key which will be common to all windows systems. The registry path you have is related to the group policy processing which will be different for each machine, so it will be difficult to script. Unless your in a domain I would avoid group policy.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Terminal Services]
"SelectTransport"=dword:00000000
"fServerEnableRDP8"=dword:00000001
Place that block into a text file named settings.REG file. You can double-click it or just commit it with:
regedit.exe /S settings.REG
The /S makes it silently install to the registry for scripting needs. I added "selecttransport" because it enables UDP transport for RDP traffic. With this .REG file you'll have the same settings in windows 7 as is default in windows 8.1.
-Ben