According to FCC regulations, you will have to have an qualified service person install a crystal and check the transmitter for proper operation. If you are not in the USA, then FCC regulations don't apply.
Great Planes operate the factory service center in the US. They have fixed charges for things like channel changes.
www.futuabarc.com
You can also send it to places like Radio South in Florida.
It will probably work OK if you use the corrrect type of crystal on any channel. The closer you are to the original channel the better, provided the radio worked OK before the crystal was removed.
If it doesn't work OK, and your model causes some damage or injury, the AMA could deny your claim.