Ouch! I just took the skins off a 1998 S70, not fun either. There are more hog clips than you can count. 4 on the very bottom which you found. It is the front of the seat that is the problem: There are 5 hog clips on each side, running up the inside seam of the side bolster, the first on is about 2 inches above the seat. If you pull too hard on the seat cover, the metal rod the clips are attached to will pull out from the foam - foam is all that is holding the rod in place.
There are a couple more on each horizontal seam farther up the seat.

On both of my seats, the plastic push tab for the headrest lock was still locked in place. A hard push with my thumb resulted in a small 'snap' and then the tab could be pushed down to release the headrest.

Needless to say, work on this with the seat out of the car. The seat position should be just about 90 degrees, makes it easier to cary and remove the bottom clips.

I used 4 inch zip ties to replace the hog clips. I suggest using 6 inch long zip ties, much easier to work with. A pair of dikes wirks well with cutting the hog clips and removing the excess from the zip ties.

The mechanism for your seat back is in the rear of the seat, so first get your arm up there and see if you can replace the cable without taking the skin off. That would be the most efficient and you wouldn't need to take the seat out of the car? Just slide the seat forward to give you some floor space in the back.

My garage air temp is at 20F, don't bother coming up here!!!
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My name is Klaus and I am a V♂lv♂holic