An interesting question , but i think it's quite useless because a region locked (RPC2) DVD player will not open or play dvd discs that have a different region settings as far as i know.
Your playback software will pop up with a message to either change the region or eject the disc.
If you choose to change the region settings , this will be done in AT LEAST 3 places :
1 - In the drive itself (except when it's RPC1 or automatic-reset RPC2)
2 - In the operating system (except when it's fooled by another program)
3 - In the playback software (except when it's fooled by another program)
What you could do , is to make your drive region free (RPC1 firmware) or install a package that makes windows think it's region free (AnyDVD for instance).
Another fun thing is DVDShrink. When you open a dvd disc in dvd shrink, let it analyze and you perform a backup ; You can choose the region settings. If you left this default (instead of tagging all regions or the region free settings) it should show you the current region(s) in which the original disc was set.