Unless he has a Multiplex crystal based radio, since those are certified and legal (in the US too . . ) for end-user crystal changes. It all depends on how the Mfg. got the radio certified . . .
All the rest, by todays technology, should be totally safe to swap, but that doesn't get past the burocratic B/S prohibiting changes in the US. The same basic modules are magically safe and legal to change in other countries . . . The power levels in R/C are so low, that the current brand of modules are broad-band enough that I doubt that even the factory tunes them when they load a crystal - they most likely just peak 'em up in the center of the band.
- Tim
ORIGINAL: bruce88123
He's from Illinois, that makes it illegal. Case closed. IF he has a MODULE based system it is legal and safe for him to swap complete modules.
Whenever changing a RX crystal (legal in all cases) best to use a crystal from the original manufacturer.