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I recently started supporting Windows NT for my company. My first task turned out to be an interesting issue. I arrived at one of our offices that had an NT server (PDC) and about 40 workstations. My plan was to replace the existing PDC with a new NT server that I'd configured as a PDC. I concluded that the best way to make the replacement was to add the new server to the network as a BDC and synchronize the accounts and scripts to make the job easier. The only problem I had to address was deciding what to do with the SID (security identifier) issue. I couldn't just change the domain of the new server and add it to the new domain as a BDC. Fortunately, I was carrying a copy of System Internals' NewSID software, which can synchronize your system with a domain controller and change the computer's SID to match the ID of any connected domain controller. When I was certain that my NewSID idea would work, I tried to synchronize the new PDC with the old one. After several failed attempts, I figured out (i.e., I read the manual) that I needed a BDC to synchronize with the old PDC. Now I was facing a new problem: How could I demote the new standalone PDC when I didn't have a BDC? I assumed that a small Registry change must be responsible for demoting a PDC to a BDC, so after I researched this subject on the Web, I discovered that such a setting does exist (for more information on this setting, go to http://188.8.131.52/ mirror/www.nthelp.com/pdc2bdc.htm).
Microsoft doesn't support this change, so I suggest that you back up your Registry before you attempt this Registry edit. Using a Registry editor, go to HKEY_LOCAL_MACHINE\SECURITY\Policy and change the PolSrvRo setting from 3 to 2. (To make this change, you'll have to change the security access on the SECURITY key.) When you reboot the server, NT will demote it to a BDC.
Although I've tested this change on my small environment and it worked great, your results may vary. Try this procedure at your own risk (neither I nor Windows NT Magazine will be liable for any lost or corrupt data resulting from this procedure). In any case, this Registry edit can be an easy solution (unfortunately, I didn't know that when I switched out my PDCs, and I had to reinstall the domain controller as a BDC so that I could add it to the domain).