Hemming them is totally possible. The tailor will have to take out the inner gaiter/cuff thingie and hem the outer shell. Then they stitch the gaiter back inside the pants. I can sew well enough to be dangerous to expensive clothing! But I've looked inside my snow pants and it's totally doable for a skilled tailor--which I am not. I'll hem my jeans but leave serious sewing to the pros. Do be warned that if you shorten them too much it will throw off where teh knee break is, which can be problematic.
Tailors can do amazing things with clothing, try to find one in or near a ski town and it should be no problem. I spent enough time and money altering my regular clothing I can't bring myself to do it with my snow pants.
lol I don't live in a ski town, I guess I'll bring an older pair to them to see what magic they can do.