I'm not sure of this but if the ores can be managed via Thermal Expansion, there is a way to force retro gen of the ores that are missing with Thermal Expansion, not sure exactly how it works in Thermal Expansion 3 but there was a file in Thermal Expansion 2 in the config folder that adjusted the ore gen of anything in the game, maybe there is a way to handle galacticraft stuff there but you would probably need to add the ores related to galacticraft and their id's to the file for it to work if its still like it was in TE2...