Well, I've had both happen to me. Sometimes, the editor leaves a note and requests that I change something in a specific way before final submission. Other times, they go in and make the change themselves within the body of my article, but they flag it to my attention before I officially give them my approval to publish it. And, on other occasions, they'll just go in and make the changes, and I won't see their edits until the piece has officially gone online as published within their Publication.