Is it possible to change Roving rn-171 WiFly module device configuration through SPI and not UART?
Try asking the vendor support, there is SPI firmware for RN171 module available on request. 

With this firmware on the WiFly you can use SPI directly instead of UART.

The documentation for SPI (e.g. pins, configuration commands) is not avilable on the www AFAIK, so you need to contact support to get this.