I don’t know, honestly. I rarely see it at restaurants, and it doesn’t apply to me because I’m not picky and I’ll take the meal however it’s normally prepared. That said, I would be miffed if I couldn’t get something I wanted for silly technicality reasons. But I might expect to pay more.
For example, “Sandwich combos come with chips, substitute fries or tots for a dollar more”. I’d still expect to be able to get a side of coleslaw or chili if I asked, I just wouldn’t expect to get it at the regular combo price. Like at McDonald’s I can get a double cheeseburger with special sauce, but I wouldn’t expect to get it at the same price as a Big Mac. It’s just common sense, to me. If I want roast beef on rye, I won’t order the Dagwood sandwich “without ham, without turkey, and put it on rye bread instead of a hoagie”. I’ll just order roast beef on rye and pay whatever that costs.
So basically, in my mind “no substitutions” means “our combos are priced based on what they come with, if you want a different combination of items and toppings, you may have to pay a la carte prices for that order” rather than “if you don’t see the specific combo you want on our menu you’re SOL”. But like I said, I literally have no experience bumping up against this rule because I take it how it comes.
I said “you can remove ingredients”, but I’m going to qualify it - you can remove easily removed ingredients e.g. if it’s fish, chips and salad, you can skip the salad or the chips, but you can’t ask for no tomato in the salad.