Adding additional tests?

<p>I registered to take the Spanish Subject Test May 5th and now would like to add the Biology test and either the Math 1 or Math 2. It says on the SAT's FAQ page that "if you would like to add one or two SAT Subject Tests (other than a Language Test with Listening) you don't have to contact us. You can just add them at the test center."</p>

<p>I know, seems straightforward. But I just wanted to make sure it's true. Has anyone done that before? I mean, theoretically, what if they ran out of the particular test I want to take? And also, how would payment work for that?</p>

<p>Thanks for the help :)</p>

<p>From [SAT</a> Subject Tests - SAT Test Day Procedures](<a href=“College Board Will No Longer Offer SAT Subject Tests or SAT with Essay – College Board Blog”>College Board Will No Longer Offer SAT Subject Tests or SAT with Essay – College Board Blog)

Further down the page it states that you can change tests on test day. From this, I assume that if you want to change tests, you simply flip the book open to the appropriate page.</p>