Ok, please someone correct me if I have this wrong:

A-it is illegal to change a tx crystal yourself, like the small pullout crystal found on the Futaba 6EXA
B-it is legal to change a module that houses the crystal like the Futaba 9C allows
C-it is ok to do B only if you stay within your low (12-34) or high (35-60) freq band

Question 1: I've read here many times that the low/high issue is probably just clever marketing. This thread seems to suggest otherwise?
Question 2: If Q1's answer confirms there is in fact a high and low band and once set from the factory, a device must remain in its band, can you plunk in a high band module into an originally low band tx, like the 9C again seems to allow?
Question 3: What about receivers? Must they also remain in their respective band?

Thanks guys. I've been looking for a definitive answer to these questions for a while now.