This documentation states that the CE and CSN pins can be specified. Can I specify A0 and A1 as these pins?
Yes, you can. The mirf library is using the regular arduino functions
digitalWrite to manipulate the pins. So A0 and A1 should work as expected.
Please note that when you use SPI (which the NRF does), you have to use pin 10 (SS) as an OUTPUT (as to not put the AVR into SPI slave mode).