If you are not admitted EA and postponed to RD, you can submit a new score:
" If I was reviewed as a test flexible candidate during Early Action and I was not admitted, can I change my mind and report an ACT/SAT score for consideration after being postponed into the Regular Decision (RD) pool?
- Any postponed Early Action applicant or applicants who are applying RD may self-report a new ACT and/or SAT score for consideration as their application is evaluated for a final decision as long as the score is reported prior to the Feb. 1 application deadline. This includes students who initially asked to be evaluated without the consideration of an ACT/SAT score. We would also encourage these applicants to submit first term senior year grades for consideration."
from Application Changes | University of Michigan Office of Undergraduate Admissions