This has been discussed (and argued) a million times; and will be a million more.
In the US, you are not supposed to change a transmitter crystal unless you have the equipment and skills to verify that it is actually transmitting on frequency (within tolerance specified by the FCC)
See page 7 in the manual. If you don’t have the manual, here’s a link to it:
http://www.airtronics.net/VG400%20and%20VG600.pdf
So, it needs to go to a qualified person for the swap. If it doesn’t pass the frequency check after the swap, the tech will adjust it until it does pass. Airtronics
recommends having the receiver retuned by a tech but there is no FCC requirement to do that.