Stumbling on this thread as I have the same problem. I believe the "solution" by Charles Kenyon is not quite an answer to the question (and I'm still looking for one).

Putting a line break before the page number within the footer indeed has the same effect as changing the margin (i.e. it pushes up the text, instead of pushing down the page number, hence as noted by CK leads to repagination).

How to lower the page number within the existing margin (not pushing up the text, but pushing down the page number; no re-pagination)?