Do you know any such MOD? Its a very handy feature - how phpBB missed it. I guess its available on other forum scripts. If you can then add it in to-be-implemented list so hopefully next update of phpBB has it built-in.
I want to ask which of Group and User permissions is preferred? I mean if a user is in specific group & at the same time I set his user's permission. Then which one will apply - User Permission OR Group Permission?