After you promote a DC, the DC's DNS suffix does NOT match the domain name that it belongs to?

You can NOT rename the computer on the Network Identification tab.

You may receive NETLOGON events (ID 5781) or other dynamic registration errors in the System event log.

This disjoint namespace behavior happens because the Change primary DNS suffix when domain membership changes check box was NOT checked before you promoted the server.

See tip 2701 ยป Upgraded DC's DNS suffix does not match the domain name?