I have an idea for that. First, you need a badge awarded to users with at least 1 “accepted answer” - I think there is a default one for that. Then you can use the Automation plugin. and its built-in automation task, called “User Group Membership through Badge”. You can set up the automation to pull people in based on their badges, and then push those people into your designated Category Experts group, and you should be set. I haven’t tried it myself though.