To clarify, the Futaba info about changing frequencies in to ranges is for RECEIVERS, not transmitters. I cut/pasted the relevant info below. Note that the info about receiver channels is for FUTABA ONLY, check with the mfg for other brands. The transmitter info applies to all brands (its FCC regulation).

http://www.futaba-rc.com/faq/service-faq.html#q2

For a unit with crystals: We CANNOT recommend changing crystals to a different frequency. Changing the crystal on your transmitter is illegal unless you have the proper license. The FCC has established guidelines for the modeler's safety and for the safety of spectators. For safety and FCC reasons we must request that both TX and RX be sent to the service center to ensure proper crystal change and retuning to the new frequency. Crystal based radios cannot be converted to another band without parts replacement, and may not be able to be converted at all. Certain radios can be converted, for example, from 72 to 75MHz. Please contact the service center for any other conversions.

The applicable Federal Regulation is as follows:

TITLE 47--TELECOMMUNICATION COMMISSION (CONTINUED)
PART 95--PERSONAL RADIO SERVICES

Subpart E--Technical Regulations
Sec. 95.645 Control accessibility.
(a) No control, switch or other type of adjustment which, when
manipulated, can result in a violation of the rules shall be accessible
from the transmitter operating panel or from exterior of the transmitter
enclosure.
(b) An R/C transmitter which incorporates plug-in frequency
determining modules which are changed by the user must be certificated
with the modules. Each module must contain all of the frequency
determining circuitry including the oscillator. Plug-in crystals are not
considered modules and must not be accessible to the user.



http://www.futaba-rc.com/faq/service-faq.html#q198


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.

For info on changing to another FREQUENCY BAND (ie. changing a 72MHz receiver to 75MHz), please click here.