I wouldn't venture into the IT world until you're fairly sure you have the correct span, and pitch for the thumb hole.
It's easy to change thumb size, because that just requires one new Slug-it which will work in all of the balls drilled the same.
But if you want to modify thumb pitch, or span, all balls would need to be modified, since the pitch/span determines the big hole drilled into each of the balls.
You can put very minor pitch, and span changes into the Slug-it, but again, very minor.