Like Phoenixangel said, it is not just an Opps, but it is illegal to change the freqauency of a RC transmitter by changing crystals. The RF stage of your transmitter is tuned to match the frequency of the the crystal. When you change crystals, the tuning is not longer valid. FCC requires that any frequency change be made by a FCC Certified tech.

The TX is FCC certified as to frequency and band width. This certification is on the RF stage of the TX. On Tx's that have RF modules, IE the Futaba 9C is one, the certification is to the Module, not the transmitter. In that case, you can just pop a RF module out and put in a different frequency RF module. I do this all the time. The Attack though is a TX that doesn't have modules, so the work must be done by a FCC certified tech. It doesn't have to be done by FUtaba, but their rates are good and you have a known good TX when they send it back.

Don