Start Playback from Plugin

It would be great if there were a way to start/stop playback from plugins, especially if this can be done for a secondary/temporary score instead of the current one.

I'd like to be able to write a plugin which does the following sequence of things:
1) It generates some temporary score (ideally it wouldn't show up in the tab-bar, but it's probably not a big deal if it automatically vanishes),
2) It populates that temporary score with stuff from the current score (e.g. based on the current selections)
3) It plays back that temporary score
4) The temporary score is deleted

With functionality like this, it would be possible to hack up the following plugin ideas (even better would be if functionality like this was built in, but being able to prototype these this way is good enough):
i) A tool to check on the harmony within a short region - Ideally, I'd like to set two markers and get it to play everything in that region at once. Even better would be if I could then click through a list of little screenshot-images of alternative arrangements of those chords and hear them played back, to choose my favourite version

ii) A tool to make it easier to preview a selected snippet with different instruments to find the best fit - The current workflow for changing a part to another instrument is cumbersome. I can temporarily test things (before "properly" changing it via Staff Properties) by opening up the mixer panel, and changing the "sound", then refocussing the main window, rewinding the playhead, and pressing play. But each time I try another sound, I have to again refocus the window, rewind, and press play (i.e. 3 clicks too many). I'd like to be able to just change the sound, and press a button beside the sound selector.

iii) A list of rehearsal marks, that I can use to quickly quickly start playback from (+ with the default option to reset the playhead back to that point after each run through)