Recently I’ve helped a few clients who want to submit their AMCAS now, but are starting compelling extracurricular activities this summer. I do not recommend describing an activity in your AMCAS that you have not yet started. Doing so can make the reader think you feel your candidacy is weak – that you are grasping at straws. One thing you can do is send an update letter later. You cannot, however, submit one through AMCAS; it has to be sent individually to each institution.
Contact me for editing help. I complete all of my own work quickly and effectively.