Replacing eyeball returns

My pool has flush mount eyeball returns that I would like to replace with a different type that makes it easier to adjust. The retaining ring that holds the eyeball in place has two nubs on it and these have deteriated over time so they cannot be adjusted. I have yet to find a wrench that fits these. My question is how do I remove these? From all of the pictures I have seen there is a nut like structure on the back end that is wider than the head. The pool plaster is around the head section and it looks like if I try to remove it, it will damage the plaster. What are my options?