That may not be the complete solution. Just as an initial test, I configured dolphin the way I want it. Closed and reopened to make sure it is keeping it. Then I closed again, made dolphinrc view only, then re-opened dolphin. It complained that the file could not be changed but opened up. I made a config change to something I didnt want it to retain, then closed and re-opened dolphin but it still had the unwanted change. So even with that file set to view only, it is keeping config changes.
if not then it could be that the change is stored in another file or you are getting interference from ~/.cache/dolphin/
i don’t think preventing dolphin from saving your changes is the way to go for this goal.
your best approach would seem to be a snapshot scheme to capture all the relevant dolphin files when you have it they way you like it, then restore that snapshot each time you open dolphin (discarding any changes saved in the interim).
this is a list (complete?) of all the files dolphin touches when it’s being used, so these might all need to be managed by your snapshot process.