Great question. I've often found myself wondering about similar things when making use of my computers search function. Being able to scan an entire document for a single word or phrase is immensely powerful.

My main point of reference to answer your question would be a book by Ann Blair called 'Too Much To Know', which studies knowledge gathering and categorisation in Renaissance Europe. The closest practice to an 'undo' would have simply been to paste over parchment with a new blank piece, or to annotate the old text with whatever new information you wanted to replace it with. 'Striking through' text alone probably has an interesting history; try searching for an historian named Antony Grafton, who has done some amazing work on apocrypha in old books.

If you're talking about this on a more philosophical level, as in not just in writing, but the broader idea of reversing an action once it's been carried out, I'm afraid I can't help you. There may well be work on this, but I haven't come across it.

According to the Oxford English Dictionary, the word "undo" dates to Old English, so before c.1150.

It could mean "to reverse, cancel, unfasten". So in the sense of "unfasten", you could undo a button, or a shoelace, or a knot. Or in the sense of "cancel", you could undo a debt, or a contract.