Agreed. I like to mix and match, time signatures as well. I use Logic and it sucks when it comes to working with different files. I have to create a master using everything I want to draw from, then piece it together. This works, but limits you to the music you have included in the master. It is maddening when you want something from another file after the fact.
For a score, and to be time efficient, it seems best to keep all cues in a single project. Then it is easy to cut and paste as needed. I think work flow is very personal as to preferences, but driven by your choice of DAW. Wish there was a steering committee for developers to take feedback from us on these things.
I also have to comment on painting a picture, our art department, SpaDogs, creates original watercolours, and these can be changed and updated, So it is not a moment in time, but fluid to a point, and even erasable depending on the paint and process.