Help! disable nickname register on service discovery

hi
i using the ejabberd server but one big problem

1. how to disable nickname change in muc ? (just realy Jid can Join in room)
i read the most topices about and editing the config file to below but not work!

allow_visitor_nickchange: false

2. i want to disable register nickname on service discovery conference but i dont konw to work!

please help
very tnx