I was struggling this morning with the same issue. What ended up working was
adding a section break (next page) after the last character of the page
before the one whose footer I want to alter. This caused the last sentence
to become full-justified. After fixing that, I added the section break (next
page) again, which had the effect of inserting a blank page with a header and
footer before the one I wanted to change. I turned off same as previous on
this page and changed the footer. Then I pressed delete once to bring up the
text from the bottom page and the footer was as I wanted it to be without
having changed any of the other pages. Kind of a pain, but effective.

"publisherm" wrote:

I need to use revision bars for changes to a document. I need to change the
date in the footer on pages where I make changes. The document has several
section breaks. On pages where I make text changes, I go to footer, and turn
off "Same as Previous." Then I update the footer date. But this change
automatically gets applied to other footers throughout the document.
Can you help?
Thanks