Assume I have a piece for multiple players in 4/4 and I want to change one bar to 7/8 or 9/8. Is there an easy and efficient way to remove or add the eighth note beat for all players?
Not really as yet, no. You could make a marquee selection around all of the instruments at that point, and with Insert mode on, deleting the note there would remove that eighth note’s worth of time from each of their voices.
I’m sure you will come up with an elegant, simple solution for this in due course. Contemporary concert hall composers in general love time signature changes, and they jump back and forth in a score, testing things out and making changes all the time. So from a composer’s perspective this is very important functionality.