I don't know that it is possible to add a specialist slot to a building that already exists, as you can't currently modify a building's core via policy. We can spoof it with a unique Tradition building that only gives an engineer, though.
Let's also strive to keep policies as 'simple' as possible. Building diminishing returns and/or factored values into policies and yield management gets really code-heavy very quickly. The key to policies for the CBP isn't to completely revolutionize the way that each tree works, but rather balance them against each other. The trees don't have to be game-changing or utterly novel to be good or interesting. Also, remember the AI. If the AI can't understand it (easily), I'm not adding it in.
G
Let's also strive to keep policies as 'simple' as possible. Building diminishing returns and/or factored values into policies and yield management gets really code-heavy very quickly. The key to policies for the CBP isn't to completely revolutionize the way that each tree works, but rather balance them against each other. The trees don't have to be game-changing or utterly novel to be good or interesting. Also, remember the AI. If the AI can't understand it (easily), I'm not adding it in.

G