If you do use forScore, there’s white in the annotation tools which you can use like white out. And because it’s digital, it’s erasable.
When I was still playing from paper, I used to always make a copy of the score and play from the copy so that I kept a clean version, and wrote only on the copy. (With multi-page scores, I had a system of taping them together like a booklet so the copies also served that purpose.)
These days I have my scores almost exclusively on the iPad though.