Okay, something has indeed gone horribly wrong. I reinstalled Strive from the .zip I downloaded yesterday from the Itch.io page, and then disabled Aric's mod (which was tagged as active in the mod screen despite having not done the replacements in this new game version), then reset the game. When I loaded it up again, it gave me the same errors.
Edit: I deleted my appdata folder and reinstalled from scratch, and it seems to be working now. Something I did differently this time was deleting the 'important files' from their location inside of the mod folder after I moved them. In addition, I think I had...some kind of mods left over from an earlier installation of the game I forgot about, because previously I had other things in there that weren't just 'Constants.' It was probably a conflict of some kind there, and my bad.