You could have something that reduced the preload spring's length, like a RS U-turn style setup, without increasing preload. That'd make it a stiffer rate without changing the threshold.What is HSC damping? Aside from the obvious definition of compression damping at high shaft speeds, I'd define it as a reduction of damping as shaft speed increases. Adjusting the threshold in most dampers I've seen (ie. point where damping starts regressing) is also going to change the amount of damping at a given shaft speed, so yeah I'd say what I described is a HSC adjuster.
What do you call a HSC adjuster? It's not like you can have an adjuster that actually changes a damper spring rate or shimstack, all you can do is add/reduce preload on the compression regression assembly.
You know some bastard will probably run off and build/patent that idea now. Oh well.