You can use the following command via the cli to set a Scanner to trust the Control Center at the new IP:
agentconfig --add <IP address of new control center>
I think you'd probably also need to make sure a new configuration get's sent to the Scanners from the Control Center informing them of the new Control Center address, to do this I think if you go to the Administration -> Configuration -> Hosts page, check a scanner and then disable and enable it that will do that trick. Do them one at a time and then make sure communication is okay, eg. stats are updating, messages are going to the quarantine, compliance folders etc.
If you are going to change the Control Center IP, make sure you are running the latest version of the product, there were some issues with oldver versions.
Cheers,
Kevin