RE: Ever had a problem when swapping crystals?
It is not illegal by the regs you cite....thats for sure. I've laid out quite a few arguments that you and the entire FCC office would have one hell've time defeating....and I guarantee you in front of a Jury....YOU WILL Loose. Because I will have the Tx in front of the Jury for them to see.
It is, however, illegal if you operate a R/C transmitter that deviates by I think .001 or .002 (can't remember now the exact number) from its assigned frequency. Changing the crystal creates band broadening so it may do that or it may not....