Ok,this is what i found about changing crystals.

How do I change the frequency on my receiver?
Futaba 72MHz receivers are all center tuned within 1/2 or the other 1/2 of the frequency band. So, if you have a receiver on any channel within 11-35 (72.010 through 72.490), you can purchase a receiver crystal and change it to any other channel within 11-35. If you have a receiver on any channel within 36-60 (72.510 through 72.990), you can change the crystal and use it on any other channel within 38-60. However, ALWAYS perform a full range check prior to utilizing the equipment. If you have any doubts about its performance, it is always best to send it for service and let us match your transmitter (if your Tx has a module, only that needs to be sent) and receiver for maximum performance

Futaba 27MHz, 50MHz, and 75MHz are all center tuned to that particular band. Therefore, any 27MHz receiver on any channel can be changed to any other channel WITHIN THE 27MHz band, and same is true of 50 and 75 MHz bands.

AND

How do I change the frequency on my receiver?
Futaba 72MHz receivers are all center tuned within 1/2 or the other 1/2 of the frequency band. So, if you have a receiver on any channel within 11-35 (72.010 through 72.490), you can purchase a receiver crystal and change it to any other channel within 11-35. If you have a receiver on any channel within 36-60 (72.510 through 72.990), you can change the crystal and use it on any other channel within 38-60. However, ALWAYS perform a full range check prior to utilizing the equipment. "If you have any doubts about its performance, it is always best to send it for service and let us match your transmitter (IF your Tx has a module, only that needs to be sent) and receiver for maximum performance".

This came from a web page and according to what i read "it is legal" to change crystals or the company wouldn't publish it,or is the company wrong ?.