I've been wondering this for some time, and have experimented a bit but could not really tell.

Lets say your preferred repertoire is tragic, so you usually run around with a guitar or harp, etc.

What if you change your repertoire to something else, like comedic for example.

Would you do better to switch to a harmonica or something more geared towards comedic, or would you want to stay with the instrument best suited for your PREFERRED repertoire?

You want an instrument that's good with your current repertoire.

I couldn't say for certain..yet. But it stands to reason that using an intstrument that fits your current repertoire is best. Not sure if you noticed but you can compare instruments and it will tell you which is better at what repertoires.