Michael,
I don't know the differences between 6.2 and 6.3 in detail. What I would do is get the Study Guide now:
http://www.arubanetworks.com/pdf/education/SG_ACCP.pdf (which is still 6.2);
..and check again when it has been updated for 6.3 to see the differences. And then revisit the added topics.
The study guide is in general a good point to start, as it also contains some example questions that helped me in the past to prepare at the right level for the exam.
If I were to do the exam again, I would not expect huge differences, as that would make it very difficult for students with earlier experience or training to pass the exam. Also, the ClearPass solution has advanced on multiple subjects, however the basics are still the same.
Herman