nope no need to change cid ..but you need to flash 3.32/3.33 firmware for running custom ICS ROMS ..best guide on flashing 3.33 firmware and flashing custom rom is ..this thread (post #1 and post #2)How about flashing CustomRom? If I don't have CID 11111111, does it mean that I can't flush CustomRom on my phone yet, even it is rooted and have custom recovery?
remember after flashing the firmware you cant boot to your Gingerbread rom as the firmware and rom are incompatible ..but you can still go to recovery and backup your current rom and flash the new rom ..just follow the above guide ..you'll come out fine