There are definitely ink blots on papyrus. Sometimes modern historians argue about whether a bit of ink is a meaningful part of a word, or just a splotch!

You could also erase something and write over it (or leave the space blank). Erasing something on papyrus was pretty easy because it’s basically just writing on a plant. All you had to do was wipe away the ink with a wet sponge or cloth. That’s called a “palimpsest”, where old text is erased and new text is written on top of it. Palimpsests are better-known on parchment (where it's harder to do, and the old text is easier to see), but you could do it on papyrus too.

The example that immediately jumped to mind when I read your question was not from ancient Egypt, but from early Islamic Egypt in the 6th/7th century…so maybe a lot later the period you’re looking for, but papyrus production/use didn’t really change in all that time. From the Islamic period, there are lots of examples of papyrus debt records, where the name of the debtor or the debt amount have been erased, so a new name/amount could be written in (or just erased and left blank when the debt was paid).

Sources for this are:

T.C. Skeat and Colin H. Roberts, The Birth of the Codex (1983)

T.C. Skeat, “Was papyrus regarded as ‘cheap’ or ‘expensive’ in the ancient world?”, in Aegyptus 75 (1995) (later reprinted in The Collected Biblical Writings of T.C. Skeat, 2004)

Unfortunately the sources where I read about the Islamic debt papyri are in French so I don’t know if that would help you here, but they were Yusuf Ragib, “Une ère inconnue d’Égypte musulmane” in Annales islamologiques 41 (2007) and “Les plus anciens papyrus arabes” in Annales islamologiques 30 (1996).