Welcome to the Forum. The ToneTwEQ board should not require any modification to install into a bass or guitar. You will need to provide a battery and a power switch (usually a special jack). The ToneTwEQ can replace the volume and tone controls in the guitar circuit.
You may wish to try using the ToneTwEQ as a stand-alone pedal before committing to an in-instrument installation. Finding room on the instrument for all four pots might be a challenge.