SBC Games wrote a series of tutorials on building games that are easy to maintain: "Many tutorials show you how to build a game. Let’s say, you already have one. And because it is good and catchy, sponsors are interested in it. Your nice and clean code is step by step polluted with sponsor specific APIs.
In this part of series on maintainable games we will add external config file. This file will allow us to parametrize game without needing to rebuild it every time."