Assigning modifiers to keys

In the KDE Control Center there's a facility, it appears, for assigning modifiers to keys such as the Win key. You get to it via Regional and Accessibility / Keyboard Shortcuts / Modifier Keys. That screen has a panel entitled "X Modifier Map", which says which modifiers are associated with the various shift keys. The problem I have is that I can't figure out how to change the settings in the Modifier Map table. Clicking on it highlights a row, but nothing I type seems to have any effect on the table. What I'd like to do is to make the left Windows key be a Super shift and the right Windows key be a Hyper shift. Does anyone know how I can do that?