The consumer collective-action economic effects of that boycott changed nothing. What did change things was the government action it triggered:
> Pressure increased across the country. The related civil suit was heard in federal district court and, on June 4, 1956, the court ruled in Browder v. Gayle (1956) that Alabama's racial segregation laws for buses were unconstitutional. As the state appealed the decision, the boycott continued. The case moved on to the United States Supreme Court. On November 13, 1956, the Supreme Court upheld the district court's ruling, ruling that segregation on public buses and transportation was against the law.
also keep in mind that the segregation rules were unpopular with the bus companies themselves (think about the infra you need to enforce segregation), as soon as the court ruled against the local laws, the montgomery bus company was rushing to flip over to desegregated.
> Pressure increased across the country. The related civil suit was heard in federal district court and, on June 4, 1956, the court ruled in Browder v. Gayle (1956) that Alabama's racial segregation laws for buses were unconstitutional. As the state appealed the decision, the boycott continued. The case moved on to the United States Supreme Court. On November 13, 1956, the Supreme Court upheld the district court's ruling, ruling that segregation on public buses and transportation was against the law.