As long as your DNS is flying right (which is needs to for Exchange to be working correctly anyway) changing the IP address assigned to a Unity box wont have any effect.
You need to be in a domain before you do anything with Unity - Exchange and AD and SQL all need to be installed and working before you install Unity, which means you have to have the domain issue (i.e. joining an existing domain or installing your own DC/GC for a VM only deployment) before you get started. You can't change the domain later - that requires a reinstall.
