You could take the "magical" aspects of the gnome and make it more "fiendish" - instead of speak to animal, speak to fiend for example. Or replace minor illusion with fire bolt?
I particularly like that idea. That would be a fun one.
Also, to [MENTION=6787503]Hriston[/MENTION], I agree. A template for turning a creature into a fiendish/celestial/maybe-even-far-realm? Would be cool. During my looking I saw that there were infernal forms of a few races, essentially the Tiefling version of those races, but they had no gnome version on the list.