Sysinternals retired NewSID a utility that changes a computers machine Security Identifier (machine SID). I wrote NewSID in 1997 (its original name was NTSID) because only tool available at time for changing machine SIDs was Sysprep tool, and Sysprep doesn’t support changing SIDs of computers that’ve apps installed. A machine SID’s a unique identifier generated by Windows Setup that Windows uses as basis for SIDs for administrator-defined local accounts and groups. After a user logs on to a system, they’re represented by their account and group SIDs with respect to object authorization (permissions checks). If two machines’ve same machine SID, then accounts or groups on those systems might’ve same SID.
Full Article: Mark's blog