Forgive me for bumping an older thread, I just wanted to throw an opinion in on something that has bothered me since I read Your Story.
Lawbreaker shouldn't be a power IMO. From reading the novels, breaking the Laws doesn't make you stronger at magic. It changes your personality, makes you want to keep breaking the laws. It's a temptation, one that will eventually turn you into a bloodthirsty monster that is less likely to show restraint in how you pursue power. Like all the hoops that Sells was willing to jump through to power his curses. That's much more of an RP thing and I feel that it's much better covered as an Aspect, perhaps as part of your Trouble. Being a lawbreaker carries just as many social implications and combat ones. As an Aspect, it can be used as a Compel too. It can be tagged and used against you in certain instances. Look at all the grief Harry caught from being a known Lawbreaker. It can be used as a positive in social situations. If you are making an intimidate check, tagging a Breaker of the First Law aspect is a solid move even if you are repentant.
The only way I see Lawbreaker as a power is as a -0 refresh choice to reflect the taint on your aura that certain people can detect. Like Marked by Power but with less upside.