FYI - The AI does not completely ignore DefaultColonyTypes.txt as I have heard here. If you add Homeworld into this text file, you can then add it to Default_AI_Planet_Types.txt and the AI will use it appropriately. I don't know for sure if "new" homeworlds can riot or not.
That's interesting. Maybe I can tweak it a bit for my AIs.
__________________
For, in the final analysis, our most basic common link is that we all inhabit this small planet. We all breathe the same air. We all cherish our children's futures. And we are all mortal. - JFK
The flag that marks HWs as unable to riot is independant of the colony type. It is turned on for the HWs when the game starts, and can never be added again mid-game. You can make new colonies have a type of Homeworld, but they do not count as Homeworlds for happiness purposes.