I am personally more comfortable with doing a new dcpromo on a virtual machine and then demote the physical (after if needed moved FSMO roles and changed all DNS pointers from clients). However, depending on the environment the DNS part could take some work to identify all static pointers to the old IP.
If you first make sure all replication is in fact working (run repadmin /showrepl *) - paste the result here if you need help with verify - and then restart the VM into directory service restore mode (make sure you know the DSRM password!), do the conversion, make sure there are no physical network connectivity on the original machine - it should be safe for you to then start the converted VM. Be also sure to verify that the replication does work with the repadmin command above.