Once an application is verified and transmitted, withdrawing from a program is no longer possible. No matter if you tell the school your are no longer interested, your AMCAS application is already marked as ED.. If you were to add schools you would be in violation of agreement you verified when you submitted AMCAS. To do so would risk a "nuclear response" from AMCAS that could include banning. In that case you would take the proper nuclear blast position with your head between your knees kissing your a$$ goodbye