On your nodes

If your server has changed of IP address you have to modify /var/rudder/cfengine-community/policy_server.dat with the new address

Then you force your nodes to send their inventory while running /var/rudder/cfengine-community/bin/cf-agent -KI -D force_inventory

In your Rudder UI, you should now be able to accept the nodes.

Your configuration is now totally migrated.