It's a lot simpler then that:
- Use DCPROMO to make a new Domain Controller.
- Move the Functional Roles from one to the other.
- Schema Master (from the AD Schema MMC)
- Domain Naming Master (from AD Sites and Trusts)
- Relative ID Master (from ADU&C)
- Primary Domain Controller Emulator (from ADU&C, only useful for NT services)
- Infrastructure Master (from ADU&C)
- If needed turn on DNS services on the new DC.
- Update any DHCP settings to advertise the new DNS server, or hand-update your statically assigned machines.
- Use DCPROMO to demote the old Domain Controller.
The concept of a "Backup Domain Controller" was deprecated when Windows 2000 released. By Server 2008 R2 there is no concept like it. All domain controllers, except for Read-Only Domain Controllers, can do everything the NT PDC used to do. People get confused by that "PDC Emulator" role, all that is is a role to name one server as the PDC for very old software that expects there to be one and only one of those in a domain.