As far as actual dresdenverse goes, I don't think the laws of magic are hard and fast metaphysical realities. The laws aren't even there to promote "good" wizards. They are just there to limit a wizards effect on the world in the interest of protecting the entire supernatural community.
It isn't breaking the law the effects the soul, I think. In the RPG, it seems very hard-and-fast, but in the books, it seems much more subtle. Losing yourself is often a slow process spanning years. And it isn't so much about the magic twisting you, but you twisting yourself, and taking your magic with you (it's what you believe, after all).
It's probably better to leave that to role-play. In fact, reading the RPG, the entire zero-refresh thing was a little jarring to me at first. I was like "I don't know if I like this explanation; it's a little simplistic". In the end, I think it's a good abstraction of that theme in the book, but it is what it is.