Yes, it's still unclear how to measure modification magnitude in general (or if that's even possible to do in a principled way) but for modifications which are limited to text, you could use the entropy of the text and to me that seems like a fairly reasonable and somewhat fundamental measure (according to information theory). Thank you for the references in your other comment, I'll make sure to give them a read!
Thank you, this looks very interesting
Thank you!
Your post was also very good and I agree with its points. I'll probably edit my post in the near future to reference it along with some of the other good references your post had that I wasn't aware of.