I want to send my GMAT score to b-schools based on my performance on test; Are you allowed to decide five b-schools after the exam?

It’s sequential, you mention 5 b-schools first then you face the test. Sometimes, by mistake if you missed to fill that form, you could get lucky and allow to write 5 schools name after the exam. But do not try this deliberately, it’s risky & you could lose your opportunity of 5 free reports.