When a recipe calls to reduce oven temperature mid-cooking, should you leave the door ajar until the oven reaches said temperature? I have always wondered this. Many recipes will ask for 15-10 minutes browning at 450f and then continue cooking at 350f. But should you leave the door open until the oven hits said lower temperature, or just reduce the temperature mid cooking and be done with it? 

What yields a better result?
No, don't leave your door ajar. The recipes have already factored in the time an oven needs to go lower. Also, as a very loose rule of thumb, many dishes tend to do better without very wild temperature swings during baking, and some of them (e.g. steam leavenend cakes) react really badly to them.