It seems like the WDK has a .dll that allows offline Registry edit:
Offline Registry Library
The offline registry library (Offreg.dll) is used to modify a registry hive outside the active system registry. This library is intended for registry update scenarios such as servicing an operating system image. The library supports registry hive formats starting with Windows XP.
This technology is for original equipment manufacturers (OEMs), antivirus and antimalware software vendors, and other application developers who must be able to parse registry hive files without loading them into the active registry.
The offline registry library is provided as a binary redistributable dynamic-link library (DLL). This library runs on the following versions of Windows:
Windows Server 2008 R2
Windows Server 2008
Windows Server 2003
Applications should link to Offreg.dll using dynamic linking.
Offreg.dll is provided in the Microsoft Windows Driver Kit (WDK) for Windows 7 and earlier versions of the Windows operating system.
Since Nuno has stopped all development on RAWREG, and noone is interested in bettering refining what I think would be the "right" way to access an offline Registry:
Maybe someone could provide a command line interface to the functions of Offreg.dll ....?