Adam replied to the ticket with "On Enhance v11 it's very complicated but on v12 it's just a few clicks in the UI.
My suggestion would be to upgrade to v12, then change the IP after the "upgrade-panel-from-v11" change the IP in the Enhance UI and proceed with the upgrade from there.
https://enhance.com/docs/getting-started/upgrading-from-v11.html
9 minutes ago"
However, the upgrade is risky thing to do for 1 node changing IP, plus the instructions linked, clearly state that all nodes should be "green" and reachable by the CP server, which isn't the case, the node is online with new IP, but CP has no idea how to reach it, because it does not have the new IP...