If I recall correctly... Futaba back in the '70-'80s certified their transmitters compliant one up or one down... giving a three channel option. Changing the crytal by the owner one up or one down did not void the compliance.

But, times seemed to have changed at least with my JR. Its manual does not offer such compliance, saying that no owner frequency changes are permitted, though a Ham ticket might provide the freedom to change frequency and adjust ones own transmitter... please don't stone me if I'm wrong, I said, "might".