To rename an existing SharePoint 2010 farm you can use this PowerShell command:
Rename-SPServer [oldServername] -Name [newServername]
Before you change the host name of your servers, you will need to use this command!
The same thing can be achieved by using the stsadm command:
stsadm -o renameserver -oldservername [oldNAME] -newservername [newNAME]
The stsadm command can be used before or after the servernames have been changed.