I found additional info on the subject at other posts on RCU. I

will put it here as a follow up.

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The way I understand it is that the TRANSMITTER's frequency

module electronics need to be tuned to it's crystal. It's OK to

swap out entire modules but not OK to change individual

crystals.

RECEIVERS however do not need to be so finely tuned; therefore

you are allowed to change crystals.

I believe the reasoning is that out of tune transmitters can

interfere with other channels and other planes but an out of

tune receiver won't cause interference because it doesn't SEND

out any signals.

The exception being you can't mix a PCM receiver with a non-PCM

transmitter. Some transmitters however, can be either PCM or

plain FM (non-PCM) so those may be used with both types of

receivers.
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You're misunderstanding matching. Matching is when someone

sends us their transmitter and receiver both. We tune the

transmitter to its maximum output, adn then tune the receiver

to the best possible reception of this transmitter. This is

done only rarely and is usually done for high $$ specialized

aircraft htat are having noise interference problems.

you can change your receiver channel at any time by changing

crystal as long as you stay int he right half of the band

(11-35 or 36-60); you are not supposed to change your

transmitter crystal at all except to replace one which got

damaged, for example, when dropping a transmitter.