The way I use Lawbreaker in my game is that the first few times someone does it, it changes an aspect that involves Lawbreaking. The GM can offer compels against that aspect that the character can refuse or accept. The compel will usually be an invitation to break a law of magic once again.
At this stage, a spell caster can dabble in Lawbreaking while it's still an aspect that they can tag and get fate points for, but they will have to spend Fate points if they want to resist the Lawbreaking lure, and it will be a disadvantage in that they may have to constantly spend a fate point just to make that choice until the GM allows them to change the aspect.
If accepting compels occurs often enough, the character should eventually take Sponsored Magic (LawBreaker). At that point, the "Sponsor" offers access to more powerful magic, and it's price for that added power is committing additional law breaking acts.
Mechanically, it means that a Wizard with Evocation and Thaumaturgy can get more power by Lawbreaking for only 2 points of refresh. It also allows a non-wizard like Victor Sells to cast spells for 4 points.
Again, this is the house rule we use in my game. It may not work for everyone's game.