I see there's another thread approuching this matter, and I agree with the origin post. Here I want to make a further point/suggestion about transcending. That is partly because I'm a Chinese, and China is more of a civilization state rather than a nation state. It is possible that you learn new things from each era while still keep some core aspects of your own. So I too hope that there's a way that you can learn new things, like new techology from each era, but instead of getting new traits, you could only twick your already had ones - use that as a balancing mechanic, and a challenge to uphold your own culture.

Or, after embrace new culture aspects, let the player chose which one serves as the dominate one, both for visial effects and for cultural related mechanisms. That is because quite a lot of cultural elements came from their living enviroment, like the climate, their land, what they eat and how they live. Even in modern era, the buildings in desert areas are not designed as same as frozen lands. That is something you can't change by just learning new things. As long as you still live there, the same factors will always apply on you. By that means, I hope the cultures could have more consistency in each era, or at least let the players able to choose to do so.