[jimbob]

Yup, you've stumbled upon the most (IMHO) important micromanaging manouver of the game. If your empire can gain 'citizens' that breathe another atmosphere, then you can move them back to the core of your empire and swap them for your race. In the process, your planets cease to be 'domed' and approximately triple in terms of the number of facility slots!! My wife always napalms alien planets and then brings in her race, but I make it a point to 'aquire' an inter-racial Confederacy as soon as possible.