Can I propagate layouts from a different dorico file?

I have a composer who made separate versions of an orchestral piece - one of them calls for 2 percussion and the other 3. Initially, I just made multiple score and part layouts with the specific instrumentation in a single file so that I could keep it concentrated in one file. But the composer found it too confusing and made two separate files and is now asking me to update the formatting to both. While I would happily take the money for the time, I really don’t want to repeat this task twice. Is it possible to duplicate the formatting from Horn 1 on one dorico file to the Horn 1 part on another file?

There isn’t a good way around this. You either need to eyeball the formatting in both files, side by side, and replicate it in the newer file, or you need to eyeball the scores and replicate the changes.

The first way is probably safer but may be slower, depending on the sorts of changes the composer’s made.

Yeah, I figured that was the case.

Not completely, but you can at least copy all the breaks over. In Engrave, lock the layout (to put a break on every system), switch to Write, select the first one, Select More to select all of them, Copy, switch to the other project, select the first bar, and Paste. Gif below: