I have done that with success on GTi MK5, and the reason why i needed to try to make something like that is beacuse one of collegues had took GTI gearbox to repair, but he could not find from same gearbox used shafts and so on, so he replaced them from some model thats not from GTI, anyway there are differences in teeth. He has repaired successfully gearbox, but cars goes to limp mode at exactly 100kmh, cant honestly remember error but it was not hard to assume that beacuse of difference calculation in TCU was wrong. So he dissasembled gearboy again to count down teeths of every gear, beacuse the TCU know exactly for every gear teeth number. I have changed number of teeths for replaces shaft, and the error came no more.