After I rearranged some footnote numbers at the bottom of a page, unwanted carriage returns stayed where the footnotes had been. So now the footnotes seem too far from the next page. What can I do to delete those CRs?

When I used the "menu" you posted and applied my choices to the whole document, the already-inserted footnotes stayed put. To me, that suggests that to make the computer arrange footnote numbers in three columns, I need reinsert the footnotes after I say how many columns I want.