As the holder of a Commercial FCC Radio License I can promise you it IS illegal to tamper with a transmitter in any manner that might change the frequency or type of modulation emitted in a manner other than that specified by the mfg. The pop-in modules that Futaba uses and Kraft used to use as well as the synthesizers are all legal as they are pre-certified as compliant to regulations. I tune and align radios for an airline every day and believe me, big brother is watching me. Even with my licenses, it is hard for me to talk mfg out of schematics for my own radios. By the way, it SHOULD be legal for a HAM operator to change his crystals on sets within assigned channels, assuming he has the equipment to verify proper operation. Go ahead and swap crystals if you wish to be guilty of a Federal Crime. I won't risk my license on it, sending it out is too cheap to risk doing it wrong.