I can’t tell you about multiple files, this is a matter of developers
If I’ll be developer, it will be different galaxies.
I thinked about this video last night
Aliens under the Ice – Life on Rogue Planets
and found way to have a civilization under water. We have creatures like octopuses, that live near the hydrothermal vent. It can moves with jet thrust, and because the planet is so cold, most part of creatures have blue or colorless blood. Our creatures have red blood. To move, they collect gas from the sources. If planet is so warm, we will have a liquid metan. Metan is explosive. When it collecting gas, metan is explodes (in small volume). And who says, we need in iron? We can find analogue of iron, that will melt in colder( like gallium or mercury).