I tried it with TMT and it works just fine in the standalone version but I use the Media Center version of TMT (uMCEDVDPlayer.exe) and that exe does not seem to care what region I set using this tool
Just to be clear, I don't launch uMCEDVDPlayer.exe directly, that exe is called from within 7MC.
Edit: uMCEDVDPlayer.exe stores it ini settings in another folder so I downloaded the source and replaced the original path with:
"%UserProfile%\Application Data\ArcSoft\ArcSoft TotalMedia Theatre 3(Vista Media Center)\"
and recompiled the .exe and now it works as expected.