L1 and C1 determine the resonant frequency. You can change either or both, but you will need some way to test whether the final frequency is accurate. An oscilloscope with an accurate signal generator is needed.
From this comment in the code: // the argument value is in microseconds per RF cycle, so 8us will yield RF of 125kHz, 7us --> 143kHz, etc.it appears that you have to choose either 7 or 8 (an integer) and neither is a good match. You can have a timer generate a signal quite close to 134.2 kHz, but you will have to write your own timer initialization code (using a different timer prescaler value).