Missing or currupted \windows\system32\config\system

I have connected the drive via usb to my laptop and able to access to retreive all my data, however, the last resort I want is to clean install the drive.

Is there a method to:

(1) access the regedit on the drive and rechange those settings I done
(2) run system restore on that drive to a previous working state.

Thanks for your help guys.