Ah, good find. If you have policies working already, then that’s not exactly the ‘Kiosk Mode’ I described earlier, this sound like more a case for Multiple Local Group Policies (MLGPO).
You won’t need Relevance to constantly evaluate a user’s group membership - instead you need to evaluate that your MLGPO is applied for whichever groups are of concern. I have some content at BigFix.me, check for LGPO or MLGPO. Most MLGPO examples are to apply one policy for Administrators and another for Users, but you can also target any arbitrary group using the group SID.
You can configure the policies using LGPO.exe. For Relevance evaluation, what I’ve done in the past is to build an Action to periodically export the registry.pol to text (also using lgpo.exe), and base the relevance evaluation on the text file contents.
In short, don’t configure per-user registries, configure per-group Local Group Policy.