If I change the xmpp_domain do I need to change my CA cert?

I have an Openfire server up and runing that is currently running as im.mydomain.com and I have my CA certs loaded and ssl is working for im.mydomain.com. The issue is we want our users to login as user@mydomain.com and currently they have to login as user@im.mydomain.com. If we change the xmpp_domain setting will the cert still work for this server? The currentl cert is im.mydomain.com whis is the name we have listed in DNS for this box. We setup xmpp-server and xmpp-client SRV’s in DNS to point to im.mydomain.com 5229 and 5222. We already have a CA cert on another server that is running mydomain.com. If I have to change the CA cert can I just export the CA cert for mydomain.com from the existing server and import it into Openfire using the keytool?

Is there anyone out there that knows the answer to this? We really want to change out our login to be @mydomain.com