Sorry but that’s not fix the actual problem where people can select “Trust Level 3” in Trust Level 1.
And disabling the selector, the avatar flair and plus editing every single user manually is not good as turning default option that nobody can’t select the group (more than staff maybe) in order to respect the base of the Trust System on Discourse.
I’m still without getting the point of allowing users to chose their group when groups are by design updated by Trust Level.
The issue probably needs to be moved to Contribute > Bug