303 Mhz Wireless Transmitter
It would probably work, but there are a few coils and capacitors on the board that may not be optimal at the lower frequency. The 315MHz version (Sparkfun WRL-10535) would be better choice. 

If your receiver is a super-regenerative type then it might already have a wide enough bandwidth to receive at 315MHz, or you may be able to retune it to the higher frequency - then you wouldn't have to replace the resonator.