Some nice work there mate, I had a similar problem with the BC Racing coilovers i bought recently, all the locking rings were completely seized up and this was after only 10 months use and a few thousand miles, so basically whoever fitted them didn't grease them at all!
I popped over to my friends engineering shop, stuck them in a big vice and tried to undo them with the c spanners but all that did was chew the rings up as the force was all concentrated in one spot. After a chat with my mate about the best approach i stripped them down until all that was left was the shock unit, lower brackets and locking rings, basically everything that was still seized, then we put them in a vice upside down clamped on the smooth part just above the threads, then out came the wd40 and some stilsons, 10 mins later everything was undone
If you decide you really want to change the height id highly recommend this approach, hope that helps.