In the US, with its larger distances, there was and probably still is some point to CB as a means of communication where cell coverage might be patchy.
CB in the UK was a brief passing fad, overtaken by easier and cheaper ways of doing the same task. i.e. cellphones with cheap contracts. Those who would have been CB-ers can now be seen texting and walking into things.
The only CB-ers who are likely to cause problems with legal users are those who want extra range and buy power amplifiers to boost output. These are untuned and increase not only the tuned frequency, but also any unwanted signal on adjacent frequencies. The transmitters tunng keeps these in bounds, but amplifying them turns them back into signals that are at a level where they do cause interference.
Over here, 27MHz toys are more likely to create problems, very few being tuned to what is conventionally regarded as a channel, but using the entire band. This is cheaper to make both for transmitters (plus they run low power) and receivers, which do not need the same number of parts to get selectivity.
Putting a 40MHz crystal nto a 35MHz receiver might well work perfectly fine. If it works, no problem, but never get the idea that it works with a transmitter. While the receiver self checks in that it either works or doesn't, there is no way that somebody without the right test gear can check what is being transmitted.