HI kvdmcanada,
The proper path to maintaining the tagged structure will not be using Replace Pages, as that only concerns the base artwork of the page. (It's the good way to retain interactive elements in the original PDF though.)
The right way is to go to the Combine files into a single PDF command and designate the pages you wish to "replace" into the updated PDF from the source PDFs. If your replaced pages are like in the middle of the original PDF, you can build the list in and order like this: Original PDF (first pages up to new content), New PDF (select pages to use as replacements), Original PDF (remaining pages). Then when you combine them, it should hold all the tagging.
Good luck.
