My rear shocks have the adjustable spring perch notches. They are now set at about the mid point. I think there are 6 notches for the snap ring. I want to lower the rear a bit. As I recall it was an easy process, but can't remember how to take the load off so the ring/perch can be moved.

I just installed Konis today and if Bilsteins are at all similar, with upgraded springs being shorter than stock by several inches.. jack up the car and remove the lower bolt at trailing arm to extend shock all the way out.. otherwise a strap could cinch the spring on itself a small amount safely. The last thing still would warrant caution though. good luck

Jack the rear up until the rear wheels come off the ground by a couple of inches. If you don't have stock springs, which I would guess by you having adjustable perches, the spring should be loose. There is an allen set screw on the spring perch. Loosen it and hold the threaded part while turning the perch. Lower it as far as you need and tighten the set screw. Adjust them the same length.
OR, you could lower the snap ring on the shock some. That would be the easiest thing to do if it didn't lower the rear more than you want.