[PvK]

Only by replacing the themes that already do this. For example, say you decide you want to replace Soul Gate Ermor with Happy Pixies of Death Theme. You could go find all the numbers for the Soul Gate units and replace them all with what you want. I'm not sure if there is a way to mod the scales requirements or effects, though. That's why I expect you could make the Happy Pixies of Death but maybe not the Happy Pixies of Life, but I haven't tried.

PvK