well, remember, Rosa Parks wasn't the 1st black person to have refused to give up her seat on a Jim Crow bus- there were a few such earlier instances of civil disobedience during WWII also- most notably with a certain young Lt Jackie Robinson of the 761st Tank Bn in July 1944 arguing with a certain bus-driver over being forced to move to the back of a bus. Which raises an interesting POD- WI this incident for Jackie actually triggered the civil disobedience component of the civil rights movement a decade earlier ?
Also, even if Rosa Parks had given up her seat, there no doubt would still have been other aggrieved black ppl somewhere in the South who would've likewise performed such an act of civil disobedience against Jim Crow, to trigger such non-violent resistance during the 1950s.