If anything like this were to happen, cultures would not be added with any particular relation to current realm borders. They would be added with relation to geographic borders.
This means that, for instance, it is likely that the island with Madina on it would have one culture, and the western mainland up to the Zuma area would have another.
Culture is not created by nobles. It can be influenced by them, but you can't just state that "because our realm has conquered all the regions out to here, that means that all these regions share the same culture!"
