Standardized tests are bullshit for the most part, they really dont measure your intelligence accurately. And there is no way to surely beat a scantron. Most tampering will either give you a 0 for the whole thing or will stop the machine and alert a person that the test needs to get rescanned. Tampering is quite obvious to the eyes, so if you do decide to do something as stupid as this, chances are, you will be caught and you will be punished. I would take a low score over the odds of that working like you hope.