That "system" bar that appears is something I find truly annoying, but there seems to be no way to keep it from appearing. The powers in it, and the order in which they appear, is entirely managed by the game itself. It's possible to assign keybinds to the slots, but I find that problematic because of not knowing for sure that the slots won't get reassigned with new power choices later. So, I still use my old "I did it my way" tray-swapping for my form-switching, and ignore the system bar. It appears for other power sets, too, but the only time I've ever found it remotely useful (so far) is the Night Ward / First Ward "plane shift" on the paths of light/darkness.
So, shorter answer, you can't manipulate that bar, and because of that, unless you really like clicking on bars, it's useless.