Debating about the transmutative properties aside, as long as the rules are being followed as far as damage, maneuvers, balance, etc., I'm more inclined to let the rest go as flavor. There are no "instant kill" special effects. They may *seem* like instant kill effects, but they still have to follow the existing rules of spell damage, invoking/tagging aspects, etc.
That said, I, too, might have trouble justifying an Evocation Maneuver which tries to place "Drenched in Gasoline" on someone using Transmutation as the explanation, without an existing Gasoline-related Aspect already in play.