I'm pretty sure it's well supported, if not explicitly stated. Harry could use his staff to bash someones brain in, and he would not have to fear any repercussions from the magical side. Now if he were to use his magic to imbue his staff with kinetic energy, making it hit harder, then it would most certainly be a violation of the first law.
And I see the same thing applying to the warden swords. If they use a sharp metal stick to chop someones head off, no questions asked. If they use a magical sharp metal stick to chop someones head off, there are going to be problems. Or maybe the warden sword is enchanted to isolate them from this. But I always read it as a completely mundane way to kill, to avoid breaking the laws themselves.
Even if you did get slap happy with Lawbreaker when you used enchanted bullets you could easily just have the enchanted bullets set up maneuvers and then cap them with a vanilla shot. The line is fine enough that it might as well not be there.
I know it depends on the interpretation (and I know, a lot of people are going to differ here), but I see the first lawbreaker as "If you think it is ok to use your magic in a way that leads to the death of a person or employs the death of a person, you broke the law."
To me, that even includes holding someone with your magic to bring down the final blow with mundane means. That includes a lot of things that would get you by on a technicality with the wardens, but not with your own mind. And the same goes with the bullets. You use them with the intent to kill someone, even if the bullets are not the direct means, you create and employ them to ensure the death of a human being. That will, in my book, taint your magic significantly enough. Maybe not for a full lawbreaker power in some of these cases, but at least a darker aspect, that will push you into that direction at one point.
Otherwise, I feel, that the laws are pretty much meaningless. You can cast someone senseless six days from sunday, but because you said you didn't use magic to do the final blow, that's ok. Yes, technically, it is, I agree there. But just because you didn't kill doesn't mean that it will leave you unchanged. Harry is always extremely careful, when employing magic against humans, at the most he knocks them out but otherwise leaves them be. Except for Justin, I don't think he ever actually used magic with the intent to kill the target human, be it directly or otherwise.