Let me try to explain. "Built-in" is commonly used to describe houses. If the stove is "built-in", it location and use were planned prior to the completion of the house. A special place for constructed for it. It is permanent, not something that can be easily removed or changed. If you buy/rent a house/apartment without a stove, you must add it. It is easy to add, easy to remove. It is most definitely not a "built-in".
Let's use the expression in another context. Your company wants to do something illegal. Perhaps you give the task to a certain department, and you name an irresponsible person to be in charge. If something goes wrong, you could say you knew nothing about it and the department head has a reputation for doing things without permission. And perhaps you even have a written rule that such a criminal act is never to take place. If you are caught, you can say that your explicit orders were disobeyed, that you know nothing about the actions of the rogue department head. You have not added anything. Everything was established prior to doing the act.
Does that help?