240 to 120 for bedroom outlets
Yes, you can. Chances are that you have a white wire connected to one of the terminals of the old 240-volt breaker, and you can repurpose it to neutral. When you put in the new 120-volt breaker, connect the black wire to the breaker terminal and the white to the neutral bus bar, removing any black tape on the white wire. Replace the 240-volt receptacles with 120-volt receptacles.