Oh, and my analogy breaks down at this point that you had asked about earlier. You can tell the receptionist that Mr. Big is not taking visititors between 9:00am and noon. But there is no equivalent for the listener.
Likewise there is no mechanism for telling the listener to NOT service a database it knows about. And with self-registration the listener will know about the databases regardless of what you put in the listener.ora file.
Well, you could have two listeners, one on port 1521 and one on port 1523, and modify the databases 'local_listener' parameter to control which one it registers with. But it would be absolutely pointless. I'm saying it can be done, but just because something can be done doesn't mean it should be done. Before implementing such a maintenance mess, you need to have a VERY SERIOUS rethink about what your real business problem is. Even to the point of asking if it is really a problem at all, or if perhaps the solution is human rather than technical. This thread has never had that discussion, and I take partial blame for not pushing that discussion earlier.