IIRC, there's no pref to edit it and you'd need to rewrite AutoAdminCheck(); to change it. What I'd do is package AutoAdminCheck and make your own system. Save the BL IDs on a different file and, when they join, if their BLID is in said file, set isAdmin to true and display the message (messageAll('adminForce', %client.Name SPC "has become Admin (Auto)"); )
I think it's 'adminForce'. I'm not sure.