How to change the SOUND of one instrument mid-playback?

Hi,

I've been losing my mind over this and there seems to be no answer. I'm transcribing a piece for the harpsichord and I'd like for the sound to change between different registers mid-piece, all while using the same soundfont I'm using for the whole score. Attached is an example of the different sounds -again, from the same instrument, so "change instrument" won't work- I'd like to use mid-piece. If I try to add another harpsichord staff, changing the sound will only change how the first staff sounds, without giving a crap about the one I just added. How can it be made? Thanks!