You do NOT need a NEW transmitter. You can have an authorized service center change the crystal for you and perform any necessary retuning/checks required. First step is to poll your club to find out what channels are in use so you can request a currently unused channel or a more lightly used channel.
It IS legal for YOU to change RX crystals and you can do this yourself. One condition exists on this IF using Futaba radios. Most of their RX are Hi/Lo band segregated and crystals must be swapped within the same "range" of the band. If you move accross the band you should also send the RX in for retuning. Futaba's latest RX do not have this limitation.