This can be implemented in one of two ways; Either as a choice at the beginning of a cycle that can influence the whole cycle, or as a regular cornerstone that persists through the whole cycle.
These would tend to show up in the first couple settlements and be more quality of life or preference based, rather than numerical upgrades.
After choosing this cornerstone pick up to 3 building blueprints, they will not be presented in the blueprint offers for the rest of the cycle.
Lizardman (or any other race) will always be one of the three races in your settlements this cycle. (this cornerstone will only appear if you havent already seen all three of your available races in this settlement)
Reputation requirements are +/- 2 for the cycle, with corresponding increase/decrease in rewards or points.
It gives a way to play "your way" through a whole cycle while giving up the chance for an immediately impactful effect this game.