Well, quite the science lesson we all got! Thanks.
Perhaps SEV could handle this by removing the "cultural traits" section from a race, and allow it to be manipulated in the game.
So instead of us reducing the race's physical attributes in the begining (or intel, or farm appt), we would make changes to the population by researching, trading, conquering, etc.
Perhaps tie it in with the colony types- i.e., your people can't live on a gas giant (without a dome, even if it has your atmosphere, whatever) unless they have the appropriate gene mods...
just a thought... well, a couple of em, but you get the idea.