<p>Can I take a different SAT subject test than I have registered for without prior permission? Or if I do, who will I have to inform of my intent to change subject tests? And what is the time frame to do so? Can I do it on the day of the test if I just feel exceptionally temperamental?</p>
<p>yes you can change it ,and yes you can change it on the test day,just tell the proctor before the test starts,and you are set.</p>