Leo, there is no way of having a flow start halfway down a page and show a title etc. that doesn’t involve either a dedicated master page of a page override. It’s inevitable.
But I assure you: if you insert or remove a page before a master page change, when the master page change moves such that it is now on the left-hand side of the spread rather than the right, or vice versa, then the other page from the master page pair will be used, and provided that pair is set up properly with the page numbers on the expected side for each page of the pair, the page number will appear on the correct side.