Possibly some misconception from the OP that the PIC has to run in some kind of synchronization with the RFM69 crystal. This is not the case, the two clocks can be completely different. The SPI interface itself is self clocking, and the SPI data is synchronized inside the RFM69 to it's own clock where necessary.
Mark.
BTW Felix, just to be clear the power-up default itself is not OFF. Note the asterisk for RegDioMapping2, this denotes a difference from the power-up state and is the recommended default setting, see page 61 which shows the power-up state is actually 0x05 for RegDioMapping2 giving 1MHz on power up. Your library turns it off.
Mark.