They are completely rebuildable. I had an 06 Fusion and DLS did my shocks for me. Fronts are easy, just make sure you have the sled off of the ground (hung, on a lift, jacked up, whatever), or you'll be pinching stuff, dropping the sled on it's belly, all that good stuff.
On the rear, taking the skid out is DEFINITELY the way to go. So much easier to work with, especially when you have to compress it to remove and put back the shocks. Which, by the way, a rachet strap works very well for. And as 2buck says, then you can do all the other maintenance without bustin your knuckles and change the slides right away. It's 1,000 times easier with the skid out.
Oh, and I just happen to have a set of brand new slides for the Fusion if you want them. Already cut down. I put them on mine, then turned around and put an extension kit on it and had to buy longer ones. So they'ved never even seen track-spin. If you want them, I'll sell 'em for $40 shipped. Polaris OEM slides, white.