Modding Question about Game Setup

[President_Elect_Shang]

In the Empire setup during game setup I see that the choices of planets and atmospheres come from the PlanetPhysicalType.txt and AtmosphereTypes.txt files respectively. Is there a way to keep the planet and atmosphere types without giving the player all those options? For example can I stop a player from picking �None� and �Ice� at game startup but keep both as potential planets for colonizing later?