They may have a “this or nothing” option. I just haven’t been able to find it yet. In fact when I placed my order there was a check box to say if substitutes were allowed and I deliberately didn’t press it. But when I got my confirmation email all the items in the list showed “substitutions allowed” and I haven’t been able to see a way to change it! I figure I’ll just see what happens with this first order as nothing terribly critical there.