Hmmm. I've never heard of changing your personal statement. From what I understand, the changes made are really only intended to be updates, such as new courses taken or new MCAT info. Or even sometimes to fix mistakes that are really significant, like stuff that could delay your verification. I don't think the idea is to use the update option as a means to make personaly changes to your personal statement. I always tell people though- just email the right people at AACOMAS to ask the question- they will be able to tell you for sure. Good luck!
You can change it. They will send the entire updated app the next Monday. I had a small typo in mine. All you have to do is change the essay however you wish and save it. You don't have to let them know or anything.