So that went well enough, and the links from the table of contents still worked, since it was one of the pages that hadn't been replaced, as did the bookmarks. So I set off to put in a few dozen links from the rest of the text... and found that they were still there, despite my having replaced the pages. I suspect that they would still be in the same physical places on the page even if the layout had changed, which might require a little fine-tuning, but in this case wasn't needed.
So... ten out of ten to Adobe for anticipating the needs of idiots like me.
New download is at the same place as the last one,
and file size is unchanged, but all that has changed is the header and footer layout and two commas in a footnote.