It may depend on the kind of sponsored magic you have.
For example, Kemmlerian Necromancy is about as evil as you can get, and in narrative terms is really just a very powerful school of mortal magic. So yes, I'd say using that to break the laws would change your soul and get you Lawbreaker.
Hellfire and Soulfire aren't independent power on their own. They enhance and alter your existing magical talents. So you're still using your own magic, you're just getting a boost from the infernal or divine realm. As such, definitely Lawbreaker for using it to break the laws.
Where things get murky is fae magic. Now, most of the beings using fae magic are going to be changelings or actual fae, so they wouldn't be affected in the same way. But envoys granted power from the Courts, such as the Summer or Winter Knight, are mortal. Since their purpose is to allow the fae courts an emissary who can directly deal with mortals, they would most certainly be expected to kill to protect their queens. I'd rule that in those cases, the power you use, since it's not actually your own, you wouldn't get Lawbreaker for breaking the laws.
Granted, being a Knight of the Fae Courts has problems all of its own...
Of course, things would get even murkier if it was a wizard who became a Faerie Knight, since then the sponsored magic is really just adding to his own power.
Perhaps that's a good way of looking at it? If the character is a magic-user in their own right, then they're subject to the Lawbreaker stunt for violations, but if they're just a mundane human without it, they're exempt?
