Of course, one of the things you can do with a minor milestone is change an Aspect. Lawbreaker makes you change an Aspect to reflect your lawbreaking; it says nothing about the changed Aspect being more permanent and unchangeable than any other Aspect. Unless you're breaking a Law multiple times every session, it's possible to stay ahead of the game and take the lawbreaker references back out.
Note that I don't view this as gaming the system but rather as what a warlock desperately trying to maintain control would look like.
Setting the Laws of Magic aside for a minute, the first time you kill someone (or, hell, the first time you get in a serious lose-and-you'll-be-spitting-teeth-while-waiting-for-an-ambulance fight) it's going to have a
huge impact on you. Even if you deal with it without going Axe Crazy, though, part of you will always be different. Not
Evil, per se, but learning that you're capable of that level of violence against another human being leaves its mark on you. After the first time, the amount of psychological trauma drops off sharply. Once you know the way it's easier to go there again, but it's also easier to deal with the mental consequences.
That said, I honestly think that the Aspect changed by an act of Lawbreaking should always have to retain some sort of relevance to what happened, similar to an Extreme Consequence. The major difference here would be 1) the Lawbreaker aspect can be altered to a different, but relevant, aspect at the next Milestone and 2) All Lawbreaking 'offenses' can be folded into a single aspect, as long said aspect covers the motivations you have for breaking those Laws... and yes, I'd also say that if you already have an aspect that would cover it, no further Aspect changes would be needed.
Just as an example, a soldier with the aspect 'Battle-Hardened Combat Veteran' wouldn't get an extra aspect dealing with violence just because he somehow learned Evocation and used a Force rote to splatter someone's head all over the wall instead of a bullet.