Changing hostname in users jid

what should i be aware of when i change xmpp.domain in the system properties window?

i want to change only the hostname part of the jid (the actual host stays the same).

after i change the xmpp.domain the existing users’ jid will change automatically?

what about rooms in conferences?

thanks in advance for the help!

i really need some guidance with that, anyone has any idea what should i do?