Brown says that they will let the student use “ScoreChoice” which means that the student can choose which SAT test date scores they send to the school. So if he does worse, he can choose not to send the worse scores to Brown.
But…some other schools on his list may not allow “ScoreChoice” and then he would have to send all the test results to them if/when he applies there. You would have to check each school’s policy individually.
Here is the link for Brown. Standardized Tests | Undergraduate Admission | Brown University
Has he thought about using his ED opportunity to ED to one of the schools on his list that isn’t Brown, and that is somewhat less selective and where he has a better chance if he chooses to ED there instead? I’m not trying to be pessimistic, but ED rates at most colleges are higher than regular rates because recruited athletes, children of big donors, and students with other “hooks” apply ED and that drives up the acceptance rate – but for these schools it doesn’t mean that an unhooked applicant has a significantly better acceptance rate in ED over RD. Tufts, for instance, might be a better option for ED.