Flashing xell only is all that is needed to obtain your cpu key. (Which you'll need anyways for rgh too) Y not just recreate a new image for jtag too? No need for the extra soldering. And somewhere on your pc, you have a backup file. How else could you have made the new image?
And yes you can on the 3.5" hd. GEting ready to do that to one of mine, as 'm not shelling out the $240 for a 2.5" 2tb drive.