As AliasVortex@lemmy.world said, all parts of Factorio are mods, and can be enabled separately. The Base mod, which can’t be disabled has the vanilla game; the Quality and Elevated Rail mods, which are from the Space Age DLC but can be activated whenever; and the Space Age mod.
I don’t know which mod is responsible for changing science and recipes though. Coupd be either side.
Did you know my profile picture is a Windows Vista background? I didn’t until a few months ago.