I've created a Mod_ImprovementsDefs and a Mod_ImprovementText. There is one item in each. My custom faction is using a modified version of the Yor tree and my new improvement replaces the Manufacturing Yor improvement. I ran the game and the Yor version is still present. How do I make it so it uses my Improvements? I cannot find any pointers in the TechDef xml file. What files controls that aspect?