this is actualy a bug since the retail version, in 1.2beta it is still not fixed
directory structrue: mods\own_mod\data\customplanets
customplanets.xml stored in THIS directory do not overrides the original customplanets file
it got to be stored in mods\own_mod\data\
it took me some time to figure out why gc2 isnt taking my own customplanets.xml, so I call it a minor bug in misleading of the directory structure.