Remotely changing DNS server list through registry

Recently I was called to help some some friends who had an unusual problem:
They demoted an old DC because they needed to raise the domain functional level, and after doing so many of their servers stopped working - they wouldn't allow remote logins, the Exchange services wouldn't start ...

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Solving and preventing "Topology Discovery failed, error 0x80040a02"

Recently our Exchange 2003 environment broke down when we demoted our last ancient DCs. We panicked and re-promoted them, but no avail. The Exchange servers won't finish loading (they'd get stuck on "Applying computer settings", while actually waiting for the Microsoft Exchange System Attendant service to finish starting ...

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