If I were to model Lawbreaker I'd just have Sponsor and an alternate Refinement power that provides specialisations in Lawbreaking. Something like this:
LAWBREAKER (Nth Law) [-1]
Description: You have broken one of the Laws of Magic and have been corrupted by it. Your magic is irrevocably tainted by this so that spells that are cast with the intent or capability of breaking that Law again are stronger and easier to cast than others. This power may be taken multiple times and must be taken separately for each Law broken.
Effects:
Magic is a Reflection: Your magic feels wrong to those with the ability to sense such things and its corruptive touch has made its mark on you. You must take the Sponsor [-0] power along with this power and you must also change one of your permanent Aspects to reflect your status as a Lawbreaker. (e.g. Magical Murderer, Corrupted Chronomancer, etc.)
Lawbreaking Spellcraft: Your magic is better suited to breaking a given Law after having broken it once. Each time Lawbreaker is taken, choose from one of these options:
Add a new element to your Evocation familiarity list: You may choose to add a Lawbreaking Element (e.g. Death Magic, Necromancy) to your Evocation familiarity list. You also gain one specialisation for that new element.
Gain one additional Specialisation bonus for Evocation and/or Thaumaturgy: You may take one Specialisation as described in the Refinement power. This specialisation gives a +1 bonus to any spell that could break another Law and stacks with specialisations in other elements.
Specialise in Lawbreaking: If you have a familiarity in a Lawbreaking element created by this power, you may instead choose to specialise exclusively in that. This would give you two specialisations in the Lawbreaking element, rather than the single specialisation that covers all other elements.
I'm not sure about the balance between the single specialisation covering all elements and the two specialisations if you take a Lawbreaking familiarity. It might just be better for Wizards to take Refinement rather than this power. Plus the fact that there are no Focus Items included in this power. I'm inclined to leave those as Refinement-based bonuses rather than Lawbreaker ones though. Makes more sense for Refinement to cover that since the focus of that power is on skill and knowledge rather than the intrinsic boost to black magic that Lawbreaking gets you.
I'm quite happy with the single specialisation itself though, since it covers all the other elements that the Wizard has access to at the cost of only giving a single bonus to power/complexity/etc. The alternative of focusing on Lawbreaking as its own element makes sense for dedicated Warlocks, but I'm not sure how I'd model it in conjunction with Sponsored Magic like Kemmlerian Necromancy or Unseelie Magic.