1 - at virt-who re-run it will automatically detect and add the new  content hosts for the esx servers.

2 - find the old virt-who servers  in content hosts  and remove the subscritions under their subscription tab.

3 - find the new virt-who servers in content hosts  and add the subscriptions under their subscription tab.
    Each registration key will need to have the subscriptions re-attached.

4 - restart the virt-who service to refresh the virt-who mappings