Like Michael said, samba 4 as an AD DC would probably not be happy if you just change the 'workgroup = ' line in your smb.conf (as a matter of fact, that line shouldn't exist in a AD DC setup in my opinion) the domain is more than likely embedded very deep inside of the LDB's, and I would strongly recommend against changing those, however, with sufficient backups and lots of luck you might be successful in changing it (look into ldbsearch and ldbedit if you are really REALLY brave). I think even changing every instance in the LDB's however will still not work, as during provision the machine joins itself to the domain (yes it joins itself to itself if I recall right). I would try to avoid this at all costs, but if you must do it, starting over may be your best option.
Just my thoughts, Ricky -- To unsubscribe from this list go to the following URL and read the instructions: https://lists.samba.org/mailman/options/samba