Reply To: Custom Page Numbering

Depending on how you define “break the automatic numbering,” you could just start a new section for 20.1 with the section prefix “20.” and then start a new section for page 21 after your new page(s) to resume your existing numbering. If you added or removed pages before 20 you’d have to adjust your section settings but otherwise the auto numbering would update correctly. This is all controlled in Layout > Numbering & Section Options.