Changing instruments of voices//microtonality
I'm new to musescore, this is my first post in this forum - I'm still not sure if it's the best tool for my use case, please forgive me that I didn't yet completely read the handbook.
I have two questions.
My first question is: I want to better understand, say, BWV 540 (the big F major organ toccata), or maybe the organ trio sonatas. I want to listen to it with different instuments playing the voices (which are really separate and individual in this material). I downloaded some scores here on musescore.org, but I have a problem with all: the manual voices are assigned one instrument (and accordingly one midi channel) and I was only able to change the instrument for playback/export for both of them. I want to assign different instruments to the two manual voices. Is this possible, hopefully, without having to select the complete first line of the score over all the pages to copy and paste?
My second question: if I want to experiment with quartertones, sixth-tones, different tuning systems, 128 notes per octave tuning etc - is this comfortably possible?
Seems not out of the box. When I add such notes to the score, they are rounded to half-tones. OTOH, when I try to import a midi files containing quartertones, they don't survive the import. So I guess I have to use addons? Which ones? Is it comfortable? Why does the program allow to add such tones and doesn't warn that they are not fully supported or suggest the installation of an according addon? Or could it be that my installation is not perfect or incomplete? I have installed the musescore3 packages from Debian Linux (testing).
Thanks in advance, Michael.