What they said. Couple other things though; it is illegal to change transmitter crystals in the US, Receiver crystals are fine. There are some transmitters (and receivers) that are set up to allow switching frequencies, either automatically in the case of some high end receivers, or through a "module" in some transmitters. (Futaba 9CAP, Hitec Prism 7 with "Spectra" module, and the Polk equipment.)

The stuff around today is truly amazing, and I believe 'silkspan' IS still available, but rarely used any more.

Good luck and have fun!
Dennis-