How to edit registry hives without live running
Run regedit,
select HKEY_LOCAL_MACHINE
File --> "Load Hive..."
The registry files are located in C:\Windows\System32\Config of the partition you are trying to edit.
Windows PE is your friend. http://technet.microsoft.com/en-us/library/cc766093.aspx
You can use it to make a customised boot CD with regedit on it that will let you access and modify the registry hives on your PC.