Roman culture for converted CK2 game

I finished Crusader Kings 2 (CK2) where I own the Roman Empire. I converted the save game and bring it to Europa Universalis 4 (EU4). If I were to create Roman Empire in EU4, regions with my primary culture would change its culture into Roman culture. However with converted save, those region would still have Greek as its culture. My primary culture is also Greek, which is what it was in CK2.

How can I have Roman culture in CK2 converted EU4 game?

In addition, in my converted game, England have Anglo-Saxon culture which is what it was in CK2. Normally Anglo-Saxon would belong to Lost Culture together with Roman culture, however right now, if I hover over it, it says that Anglo-Saxon belongs to British culture group. Is there a way to turn it into Lost Culture group so that it would belong to the same group as Roman culture?