The lawbreaking feats leave a mark that can be detected via Sight and Soulgaze, which shows who can be decapitated and who can not. The use of magic to break the laws actually turns on the person doing it, reducing their free will until eventually they're raving lunatics that are unable to do anything but behave that way. The aspects they create are double-edged, as are all aspects. Getting lawbreaker 1 makes you better at killing, and worse at any other option.
In the case of Killing, physical and mental transformation, and outsiders, it's pretty obvious who would provide the "you're better at it" part and who would provide the "and you become incapable of keeping it subtle, so you get caught/executed/self-destruct" part. The time travel and invading minds part is more problematic, but both are impossible to prove without leaving some traces and for all we know there are adversaries trying to spin off alternate realities and I'd say the Oblivion wars provide enough on both sides to result in the mind-reading lawbreaking. The unknowns are why I find it interesting as a plot point. If you assume, say, Denarians are working to encourage more killing with magic and Knights of the Cross & their boss are trying to reduce killing with magic, and the extension works pretty well with known groups for several laws, then you get interested in the remaining laws and discovering the truth behind it is a whole campaign worth of story.
