Just to be safe I would probably jack it up just enought to take the weight off the springs and axle. Backing off the bolts will probably be fine, but I'm doing this from my desk and am going by memory.

Yes, the gas skid is just short of worthless. You should see mine! I think it's part of the problem why I'm getting bad readings from my guage.

The sway bar extenders are most likely for your front sway bar. I think Calmini is the only one who makes them for the back (why I'll never know).
Anyway, it's real easy to do. Look for a shaped crossbar that attaches to both front a-arms. Get a 14mm socket and a wrench (I think that's what they are). Hold the top, and unscrew the bottom of the bolt. Keep an eye on the order and direction of the bushings if you're not familiar with that stuff. If SLR gave you new bushings, put them on in place of the black rubber ones, along with the new longer metal sleve that will allow your sway bar to return to a more factory angle with the lower-arms now at an increased angle.

If you're in the mood someday. Take off the two swaybar brackets that hold your bar onto the frame. You'll see that the rubber bushings are shot there. www.xterraparts.com has replacements for something like $5.

Oh, you should be able to rotate your sway bar by hand to get it in the right position for the new extended sleeves. Just lay under the truck and pretend you're bench pressing them up.

You might also want to jack one front tire up to ease some tension before removing your stock sway bar bolt. With one off, the other won't have any tension other than that from the shot bushings.

I'm taking breaks betwen work (rendering a bunch of 3D scenes, so if you have more questions I should be around)