once the drive has been flashed to RPC-1, updates from apple do not change its state. What i did was to run all the updates available at the time, restart, run the flash, restart again (following the instructions that came with the flasher) and then just continue using it as normal.
You can get the rpc-1 firmware from
http://perso.club-internet.fr/farzeno/firmware/ and scrolling down to where the Mat****a SR 8187 is listed.
In the readme file it does state that with some of the drives it doesn't work, due to a "non updatable MaskROM or by explicitly update-disabled firmware". If that is the case, then there's not much you can do about it, and the firmware update will simply leave the drive unchanged. So, even if that's the case then it isn't going to damage your drive (providing you follow the instructions).
If you're feeling paranoid about it though, then your best bet is going to be to just leave it be and get by, without changing the region on your drive