So, I arranged a marriage between my character and the Queen of Denmark, meaning our oldest son was heir to both my empire and her kingdom. My wife died before my character, so my son was ruling Denmark for a while. In the process he converted to Danish culture. Now that I'm playing as him and ruling the Empire of Brittania, I'd prefer to convert back to English culture, but the decision isn't showing up. I do have Rajas of India enabled and based on the wiki all of the requirements are met (I am independent, non-nomadic, and I have sufficient prestige. My capital is English culture. Is there some other restriction? (Like once per lifetime, maybe? Traits which disallow it?)