Paul, many thanks for that - the main thing is to know what needs to be done.

But one thing I don't understand: can you tell me why the url paths would need changing - is that only for hyperlinks used to get into the document set from outside, or for all of them?

There will only be one, or at most a few, url entry points to the document set, so I was hoping to avoid changing paths for the rest by using relative hyperlinks. All files will be held in the same server directory, so once a reader has got into the document set, I thought that links clicked on later wouldn't need to include a path, just the filename?