If you create a MultiStyle you should be able to use the same style but add a different realtrack to the legacy track and save that as another style to use for each substyle so at the different colored part markers you should get a different instrument on that track. So you change the part marker every 8 bars to a,b,c,d,e,f,g........
Have a look in the manual under MultiStyles, I think that is how it was done ?