Obtain the txted planet*.entity files, then look through them for the total resorce asteriods count and also the metal & crystal asteriods counts.
Add new planet types from the mods into the editor.
Edit the .galaxyscenariodef file to add in the planet types. There are two copies of this file, one in the folder where GalaxyForge is (this is the copy that GF uses to figure out what kinds of planets exist) and one in the game's GameInfo folder. If you don't update the one in the game's folder too, then the game won't know about the types .