I mean, I think it depends on how/why you're paying their sub?

If I go out for lunch with someone and they buy me a sandwich, and then I start to eat the sandwich and they're like "I bought that sandwich, so before you can eat it you have to take the ham out, roll it up, and stick it up your nose." I think we'd all look at them like they were nuts. It wasn't part of the terms. ("I am altering the terms. Pray I do not alter them further.")

But if they say, "Hey, I'll buy you a sandwich, but if I do, you have to take the ham out of the sandwich, roll it up, and stuff it up your nose", then it's on me if I accept those terms; I either buy my own sandwich or I end up with pork-nostrils.