Hey Simon! 
I get what you mean — basically a way to push changes you make inside a big full-set project with multiple songs back into each individual song project in a multi-file setup, right?
As of now, AbleSet can’t sync changes between separate .als files, so that workflow isn’t supported as of yet.
But as a workaround, you could:
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In Setlist Edit Mode (from Beta 15), right-click a song to add Descriptions, Stop Descriptions, set its color, or adjust the end-of-song behavior.
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If you’re using Canvas, there are new features coming that will allow per-song notes, as discussed here.
These won’t modify your original Ableton projects, but they’re good ways to keep reusable reminders — like your {Building} note — inside AbleSet.
Happy to hear more about your setup!
Agus