Change the SID of a workstation using Systeminternal's NewSid.

NewSID
NewSID is a program we developed to change a computer's SID. It first generates a random SID for the computer, and proceeds to update instances of the existing computer SID it finds in the Registry and in file security descriptors, replacing occurrences with the new SID. NewSID requires administrative privileges to run. It has two functions: changing the SID, and changing the computer name.
To use NewSID's auto-run option, specify "/a" on the command line. You can also direct it to automatically change the computer's name by including the new name after the "/a" switch. For example:
newsid /a [newname]
Would have NewSID run without prompting, change the computer name to "newname" and have it reboot the computer if everything goes okay.
Note: If the system on which you wish to run NewSID is running IISAdmin you must stop the IISAdmin service before running NewSID. Use this command to stop the IISAdmin service: net stop iisadmin /y
NewSID's SID-synchronizing feature that allows you to specify that, instead of randomly generating one, the new SID should be obtained from a different computer. This functionality makes it possible to move a Backup Domain Controller (BDC) to a new Domain, since a BDC's relationship to a Domain is identified by it having the same computer SID as the other Domain Controllers (DCs). Simply choose the "Synchronize SID" button and enter the target computer's name. You must have permissions to change the security settings of the target computer's Registry keys, which typically means that you must be logged in as a domain administrator to use this feature.
Note that when you run NewSID that the size of the Registry will grow, so make sure that the maximum Registry size will accomodate growth. We have found that this growth has no perceptible impact on system performace. The reason the Registry grows is that it becomes fragmented as temporary security settings are applied by NewSID. When the settings are removed the Registry is not compacted.
Important: Note that while we have thoroughly tested NewSID, you must use it at your own risk. As with any software that changes file and Registry settings, it is highly recommended that you completely back-up your computer before running NewSID.

For Further reference and NewSid download : http://technet.microsoft.com/en-us/sysinternals/bb897418.aspx