Scripts aren't PixInsight processes, so you can't take instances of them, and their parameters can't be stored anywhere that I know of. The supplied ones can be modified to make use of the Settings PJSR object to store the latest set of parameters specified (or even older ones too, if desired), but there's no easy and convenient way to store them in a place comparable to .psm files. What I usually do is take note of the relevant information into one of my process icons, like "Following this process, do a MaskedStretchTransform with the following parameters: foo -> 42, bar -> 69".