I want to create a part that contains only specific notes from the original score (e.g. All A6 and B6 notes). Does such a plugin exist, or something close to it that I can start with?

I have a score for my bell choir and would like to extract only the notes that a single player will be playing onto a separate part. I have written a plugin to color the notes within the existing score, but want to be able to separate it into parts. Assigning parts withing my existing plugin doesn't work - it seems to not be able to change note parts well. How can I move these notes to a new instrument / part within a plugin?

If there is an existing plugin that does something similar, I would love to use this as a template...