RE: Radio Frequencies-Change 40.830 to 40.835
There are no rules in New Zealand about changing xtal's. In your example a change of 5kHz (probably even 10 or 20kHz) won't make that much of a difference in the radio system performance. However going from one end of the band to the other will probably cause issues. This is because the RF output stages are tuned to a particular frequency (ie the one that it is sold with) in the factory.