Actually, once they are past a certain point, I'm okay with the students changing the kata. So, yeah, I'd adjust the kata for someone who can't physically do what I put in there. I allow stuff like a rear hammerfist instead of a rear elbow, too. I'm pretty lax about that. If the thing they do makes sense (and I often make them explain a different choice, as well as the pros and cons of it), then I don't much care.