I have a gallery type site with multiples numbered pages say 1-27. I add a new gallery page occasionally. I then have to add a new page 28 and manually copy and past the photos on page 27 to page 28, then page 26 to page 27 all the way up so that page one is empty and then I load page one with the new pics. This way the oldest pics are still on the last page.
I had the same issue and just decided to do it the other way around. Why don’t you just add page 28 with the new pictures and add the link to the new page 28 on the master page?
If you’re particular about the page order then the only other alternative I can think of is to re-link the pages on the master page (the new page 28 then links to page button 1, etc.). That way you wouldn’t have to copy and paste the pictures all over…