Well, ideally a glass bow would need very little tillering, mostly just making sure you've got a slight positive tiller and that the string tracks through center. If it comes out wrong, it is usually altered by changing the tapers and adding or changing powerlams and tip wedges. I guess you could sand the glass, though preferably you would get it bending how you want by changing the core, rather than the glass. Kenny did a bow where he uniformly tapered the glass, and it turned out well, so maybe it's fine.