SSL has nothing to do with ips.. your certs will be ok..
As far as the change over, if the majority are on shared, you should be able to change that "Shared" ip somewhere, and redo the apache conf (generate).
I don't have cpanel experience, sorry.. however I assume you would change the master ip, then goto the slaves and change those.. then modify your trust relationships to the new ip base.
I suggest RIGHT NOW you go in and modify your name servers and drop the refresh times down to < 1 hour so that you have minimal downtime. If you don't know how to do this, either ask cpanel or wait for a reply from somebody here who has direct cpanel experience.