I'd say this would work exactly the same as any other transformation - lawbreaker if you do it to them, both metaphysical and warden-law-wise.
That said, there's a loophole: if you don't transform them, but instead give them the ability to transform themselves, then you're probably okay metaphysics-wise (but likely to still have warden related problems). An example would be the wolf belts from fool moon - making such a belt isn't, itself, a law violation. (Or at least, I wouldn't treat it as one; I'm sure other people will have different opinions. And the wardens certainly wouldn't care about such subtleties.)