Parameters (Fields) once create should have a option to edit them, if you wish to add more fields to the parameter. Currently there is no option to do this
Fair, that could be helpful. We may be using "powerful" differently too: I'm referring to raw capability for the technical user, but I can also see how having a GUI is "empowering" for non-technical users, as it opens up capability that would otherwise have needed a deeper understanding of the language.
