"Psssst, when Mrs. P says to read the instructions, it's because it's a fake test! If you just follow the directions you can get an A without even trying!"

And that is that test ruined for all subsequent classes. People may not read instructions, but they will generally listen to peers highlighting that there is something unusual, or some easy way of cheating. Heck, it might become a weird group wisdom to always answer "C" because the answer scanning machine is broken or something. I've seen weirder in actual work places.