I have not done this myself but I think they have this exclusion to stop the test prep companies from knowing what is on the PCAT. I worked for one as an SAT tutor and the company would have the tutors take the exam over and over. It seems Pearsons has a policy to stop this behavior.
You want Pearsons to know that you aren't working for a test prep company but don't just come out and state it. Tell them that you want to take the test to improve your score and then state why you think you will do better this time. If you have taken extra classes, include them in the letter. If you got tutoring, tell them that. If you spent months and months working on your math or reading comprehension skills, mention it. If you can't say any of these things or point to some other reason why you are going to do better, then I wouldn't retake the PCAT until you are absolutely sure that you will have a higher score this time around. You don't want to be having to write Pearsons to get permission to take the exam a seventh time.
