How do mods work?

[ProLeetNoob]

Does the other player have to have the same mods for them to play with me? Will a save file go corrupt if a mod is changed or removed?

[Mod Sloth]

I don't know about multiplayer, but I've added/removed mods between saves without any problems, though this is definitely done at one's own risk.

[Truckin' Tom]

Yes, whoever joins you has to have the same mods installed in order to play with you and most of the mods that are multiplayer compatible mention it in the mod description. I've added and removed several mods over the past few hundred hours without issue. Just be sure to use the Satisfactory Mod Manager instead of modifying the files directly, try to stick to mods that are current and be mindful of how many mods you run at any given time, as some may cause your frame rate to suffer. Have fun.