Applying the Lawbreaker stunt can have huge consequences for a player character, up to and inclduing suddenly becoming an NPC. (Let's face it, a lot of spellcasters play on very low refresh.) I would never, ever force a lawbreaker stunt on a PC without explicit out of character buy-in from the player, any more than I would kill a PC without discussing it with the player.
No, not even with a Compel. Compels are there to create complications, not to radically and permanently alter the character.
That said, if the PC throws around a bunch of potentially-lethal evocations on mortals it may be appropriate to apply compels on his high concept and even request aspect changes to reflect how the PC constantly skirts the law and people are beginning to look at him suspiciously