RE: arthur, bg, paul, and other smart folks, a ?
Man that is a tough one. My advice would be to try it and see what happens. Instead of making a short string just twist them up for now and play with lengths to see what sort of results you get.
I will admit I am not much of a bow mechanic, I try to learn as much as I can about the bow I own, but others I am not that familiar with. We do have some good bow mechanics that own or work at shops that would probably now for sure. Or you could call the manufacturer of the bow and talk to thier tech department.
I have never done it to a single, but I have to a dual cam and a hybrid cam (CPS). If you shorten the string enough I doubt you will be able to get the cam right no matter what you do to the cables, but you might. I would just experiment and see what happens. I have done it quite a bit to my darton, messing with the string and cable length. I have put a longer string on mine, and a shorter one to make it fit my girlfriend. I shortened the draw length a little more than an inch to get it to fit her. If you shorten the string I am pretty sure you will lose peak weight, I did. And most likely lose some effeciency from the cam. That was not a concern with me since all I want to do was teach her to shoot with it.
When I have messed with it for myself I let the cams go extremely out of time and the bow still shot very well. It did not effect the performance in any way that I could tell, other than speed. This was a CPS though, I don't know how it would effect a single cam. I have not messed with my Bowtech that much. The other thing to consider is that my darton has three seperate strings, one string and two cables, not one long string and a cable.
If you are working with him face to face, I say try it and see what happens. Work on getting the bow to fit him, then see how it shoots. I would not concern myself with brace height, ATA or peak weight yet. I don't think it will effect any of them enough to make a big difference. Even if the cam is out of time I would still see how it shoots and tunes. I think for now it is more important that the bow fits him and he can shoot it well. Later he can see about getting the correct cams/modules or a bow that fits him better.
If your not doing it face to face I don't know what to tell you, it's going to be pretty tricky to get it right.
Paul