I had a good search and I don't think this has been mentioned before but appologies if it has...
I noticed that when you make a setup change during the race via the F12 menu, some text (something like "Setup changes at pit stop") appears in place of the repair damage [on/off] option. So if you make a setup change and then decide you want to change the damage repair option you have to undo your setup changes for the damage repair option to reappear and then re-define your setup changes, which is pretty fiddly in the middle of a race!
So my suggestion is that the damage repair option is not hidden when you make a setup change in the F12 menu.
I noticed that when you make a setup change during the race via the F12 menu, some text (something like "Setup changes at pit stop") appears in place of the repair damage [on/off] option. So if you make a setup change and then decide you want to change the damage repair option you have to undo your setup changes for the damage repair option to reappear and then re-define your setup changes, which is pretty fiddly in the middle of a race!
So my suggestion is that the damage repair option is not hidden when you make a setup change in the F12 menu.