You can change normally using the registers. It can work all over the full range allowed by the SIL chip.
What happens is that hoperf adds some filters that will make it work better on model range. So don't expect to have the same
performance on 866Mhz if you're using a model for 433Mhz.
Example, for the purpose of acting as a frequency scanner is it ok for a LRS I'd stick to the model frequency to get the maximum performance.