Many mobile repair shops have equipment which can re-write the IMEI back to the device fairly cheaply. If you have no EFS backup & tried flashing stock/that didn't work, you don't really have any other option.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?