One could install this image to some drive then boot another instance of XP SP3 to load the registry in the other drive. It's documented on MSDN and now that you have the registry loaded from the other installation you can make your changes.
Once the changes are made you use the process you created to recreate your new image.
This will be very advanced work.
We have a Windows XP image which was removed from one AD domain and added to another one. I am trying to find a tool or process to remove all the references from the XP image to the previous domain.
Any help is welcome.