Is it possible with any existing modcomp to have a building automatically provide a given promotion for all new units (or all new units of a particular class) within that city, but also have the promotion dependent upon techs? Example: Building  automatically gives Promotion [A] to all new melee units built in the city. After the civ discovers Tech [X], a new promotion becomes available and replaces [A] as the one automatically given by Building . I'm thinking about something such as various firearms advances upgrading units without requiring new units themselves. You simply build a training ground of ballistics lab, and when you get the new tech, all of your new firearms units get the boost from the promotion that represents the new tech. When you get the next tech, your new units then receive the next promotion. It'd also be nice if there was a way to upgrade the old units, perhaps with the earlier special promotions listed as precursors to the later special promotions. As in a unit that already has [A] can use XP to get if the civ also meets the tech requirement. Again, I don't know if anything like this exists or is even possible, but I thought it might be an interesting way to add more layers to units without requiring players to constantly build new units or memorize a ton of different units within a vast upgrade tree.