Clearly you have never run a busy restaurant, as though this may appeal to many, it would actually be a total pain for the chef, unless he is carrying an extensive and well stocked inventory. Good restaurants are like any other businesses, although the need and dependence on preparation and planning is far more real, as you are generally operating after hours and thus don't have the ability to restock during that period. Believe me, that point alone is enough to say No.
Obviously, it would also depend on the actual recipe.. I doubt that lamb chops would go down well in a Vegan kitchen and so on. It can be done, I'm sure, but in the food industry, what's often a matter of and referred to as 'bums on seats' takes priority. ie: The planned day's menu always takes precedence over an unplanned individual serving. It's a tough job trying t please people who often have little appreciation of what is involved in the industry. Mum's are usually into working that way, but once again... give them the ability to plan the meal and a genuine thanks for the effort!