the game's code is inside various objects/instances in (a version I don't have anymore of) gamemaker's script editor. If there's some way to get a different version...like, whatever re-ordered code GMS converts it to to run the game off of (if that's how it actually works? dunno) I have no idea how that is done/acquired at all. Maybe look into how people mod old GMS games like Hotline Miami?
Sorry about those soft locks! Yeah my platformers did that a lot I remember.