Wow that is awesome did not know thanks!
Without delving too deep into suspension theories, those preload adjusters are used for setting "sag" height, not for changing the stiffness of the spring. Sag is how much the bike (or scooter) sags down when you sit on it. Ideally, there would be multiple spring rates to choose from when buying a shock. But that isn't going to happen in the scooter world (for the most part). So pretty much, if you're a heavy guy, then you would crank that preload adjuster all the way up so that the scooter doesn't sag too much in the back when you sit on it. Likewise, if you're lighter weight, then you would have less on the preload adjuster. It won't change the spring rate.
Ok, moving on, my next step is to install a pair of new Carbone adjustable shocks, but I don't know how they adjust. From the factory they are set at the "deepest" setting and will only adjust to the left. As set, will they give the stiffest ride or the softest ride? Sorry, I just don't know.