Afaik, and I may be wrong on that, civs' flavors come with a random factor that is applied to them at game start. In other words, Hiawatha the Expansionist will always be an expansionist, though he may be a little more aggressive or a little more passive in different games.
Again I'm not sure but it should be possible to mod the flavors without much effort since such things are said to be stored in xml files.