When replacing an domain controller you might need to reuse computer name of the old domain controller. To do that you can create an DNS alias for it.

netdom computername current.fqdn.of.server /add alias.fqdn.of.server

If you for some reason you want to change computer name to the alias you need to run

netdom computername current.fqdn.of.server /makeprimary alias.fqdn.of.server

Reboot server for the name change to take effect and register changes with DNS.