Watch your knuckles if you adjust the spring tension with the shock mounted to the car. The brakes, the brake hoses, the uprights, the a-arms are all in your way unless you have a ratcheting spanner wrench, which I've never seen. My spanner wrench is about a foot long and bumps into everything when it's trying to rotate that nut on the bottom of the spring. You'll have to go about 3 full 360 degree revolutions of the nut to get about 0.25" of ride height at the shock and this will translate to less than that amount of ride height difference at the fender to ground measurement.
That's a lot of 1/4 turns with the shock on and I took them off to do it. I had the parking brake on and used the middle or top lug nut to hold the shock body firm while torquing the nut with 1/2 revolution movements. The spanner wrench doesn't fit tight like a socket head, so it wants to slip off. This is another opportunity to bust your knuckles if the wrench slips, so watch the position of the wrench on the spanner nut for safety reasons while loading force on the wrench. If you go only a quarter turn or two, you won't notice any difference at all. You'll see. I tried to do it with the shock on and said forget it, that way will take a lot longer to do and it'll be easier if I just take them off. But maybe somebody has a better tool to use, I don't know for sure. Look at the PIM pictures and you'll see what kind of room you have to work with. It wouldn't be very possible with my spanner wrench. Possible? Yes, maybe.