Hmm... Interesting concept. I was about to go into the fact that the spell would probably flat out kill them in the process, and you'd need to work in making a flat out new body for them, but then I noticed you had already figured that in, hehe...
Would be very difficult to pull off though for the most part, and would require a very large amount of effort, time and resources to garner a spell this powerful... One would wonder why a villain would put so much effort into such a spell, when they could use a fraction of it to just kill you... The actual splitting part of the spell would vary greatly from target to target, the loup-garou quite possibly being one of the most difficult targets by far... You would have to figure in, on top of everything else, the vast complexity of the curse placed upon them... And not only the part where they are turned into such a monstrous creature, but the complexity as well of a curse that could pass down from generation to generation, lasting potentially hundreds of years.. I forget if there is even a potential limit to how long the Loup-Garou curse can last... And you'd have that nasty monster, standing right there... Very nasty prospect... Also potentially doable, if the person had the expertise...
Now, the act would be a permanent transformation though, so I don't know if you'd have to worry about duration tables... It gets kinda weird there... Maybe thats why complexity to some of that stuff gets so high, because you have to figure for incredible durations... But for the most part, as far as flavor goes, such a major change to a person physically and spiritually would be a permanent kinda thing, one that would let you not have to worry about duration and all that...
