You can't introduce NEW magic actions past index 53. Then you'll have to make sure the spell order (In the Initial Data tab) has the new action in the menu that you want it.
Super nova can work with more effort, but that takes a degree of modding outside of WM's scope. That would require some heavy exe editing. I once did some minor editing of the Ultima animation, but the code is so convoluted that it wasn't really worth the effort. Getting Supernova to work anywhere might be worth it, however. Sadly, the function to take a snapshot of the background doesn't exist (you might be able to hijack whatever method Odin uses to take 2D stills of actors, but even that makes assumptions) and it makes a lot of assumptions about targets. All of which are true in unmodded, but hard to change by hex editing.