Maybe we can use this opportunity to add proper diff logging to registration form setting changes?

I don't like the idea of hardcoding a single case here and not logging anything else...

So basically, do something similar to what we do in update_category / _log_category_update or _log_event_update.

I wonder if you hadn't make a mistake with the latest change for log title ?
Here are the 2 logs:
the upper is with your change, the 2nd is mine, and it seems easier to filter logs on Registration Form with the old code...

Yes, it's consistent with the log messages for creation. The text there is the module, not the log subject (that's a mistake in my commit msg ;)). And if you view one of those messages, there is a button near the bottom of the modal to filter all log messages for that regform - so you see updates, creation, etc