Hi Mayur,
RRP3 and RRP4 are just receipt views where you can only change the Availability Date. I understand that DS board might be an overkill to change start dates but you can also try the Resource Planning Table /SAPAPO/RPT where you can use Forward Scheduling and the Start Date / Start Time are open to edit. If these manual changes are not too frequent, you can always delete the unwanted Planned orders in RRP3 / RRP4 and create a new ones with a strategy set to Forward Infinite Scheduling.
Regards
AK