It is illegal to swap crystals in the transmitter. (any brand.)

It is OK to swap the modules. The module contains the complete "RF Deck" and is tuned for the crystal that is installed.

Each TX is individually tuned to the crystal installed. It takes about 30 sec at the factory. (clip 2 wires on... turn on... tweak the tuning capacitor.... put on the sealing wax.... unclip the leads... pass the TX to the next guy.) The guy that tunes the TX's tunes a couple of hundered a day easilly. (then he goes and does other tasks... they don't need him to tune 1200 radios a day.)