change sound of a few notes ?

I am experimenting to try to change the sound of only a few notes on a guitar staff. Or maybe change
the sound of all voice 2 notes. The sound I'd like is a "tick" or "tock" or "drum stroke" sort of like a
metronome would deliver. The sound should be "pitch less."

I can get it for the whole staff, but not selected notes.

I want to build some rhythm practice exercises where a "rest" is sounded.

Suggestions please?