From the Source Books, Dresden Files Fiction View Point:
(Some Mild Spoilers from the Books to Follow)
The Laws of Magic only apply to Mortal Practitioners, i.e. people who draw energy from the world around them and from within themselves, not from a source. That said, those who do both: draw Magic from within themselves & use a sponsor ARE under the Laws of the White Council (Necromancers, etc...)
A Changeling is under the purview of the Seelie or Unseelie court. Their magic is not "Mortal" and isn't policed by the White Council. Another added benefit for using Faerie Magic is that it isn't conflicted by coming from a Mortal source and thus they don't have to worry about it hexing things either. All that said, every use of energy that comes from the wellspring of either the Winter or Summer Court IS a representation of power of the Queens, and as such is policed by the Queens (usually the Ladies) or their Sidhe Nobles. Above and beyond that, the sponsor will not grant power for applications that are outside their exact realm of influence. Essentially, if you want to use a sponsored magic for something that is outside the realm of effect of the sponsor, the magic either doesn't work or is greatly reduced.
In the book Summer Knight, Harry is working as an Emissary of Winter and as such puts himself in opposition to Summer, thus Summer Magic works against him the whole book, but when Murphy get's involved in a conflict the power of Summer is greatly reduced against her because she was not connected to either court.
Another instance is in the book Cold Days where Harry temporarily violates the "Law of Winter" and thereby temporarily looses his connection to the Mantel of Power he has from Winter at that time.
Now, does this mean that the White Council won't seek to oppose a Faerie Bound Changeling that is murdering people with Unseelie Magic? No, of course not, but the grievance between the combatants would be governed under the Unseelie Accords and not a by-law within one of the signatories (The White Council in this case). In the book White Night, Harry and Ramirez demand a duel with one of the signatories of the Accords for retribution based on murders the citizens of that signatory perpetrated on some mortal minor practitioners. In that case a formal Duel was offered and fought, but the signatory also had the "right" to pay a weregild to the White Council for killing the entities under their jurisdiction.
If it helps, think of Mortals and "Other Things" as citizens of different countries and beholden to the laws of their home nation. Thus fighting between the citizens of the nations can be legally difficult to sort out as what is against the law in one nation isn't against the laws of a different nation. This is also the sort of stuff that causes wars, as seen in Book Three: Grave Peril where Harry kicks off a War between the White Council and the Red Court of Vampires.