Removing mpc# at the lounge works perfectly fine. I've done it 8 times in a row and works every time. After changing your FF# you can even get a red lounge re-entry to access the other F lounge. If you're worried then go to another lounge to verify the number has been removed - they will happily confirm. If you're moving to BAEC get them to enter your BAEC# in the lounge rather than removing.