Sorry to hear about your experience with a burn. Fraxel re:pair has been shown to be effective in the treatment of surgical scars and acne scars. I am not aware of any studies or treatments on burn scars. With a keloid, a primary treatment of the keloid without laser may be first indicated, followed by the laser on the residual scar.
I do know that it should not make the burn scar worse. I would treat a small portion of the scar and observe the effect. If it improved then I would consider treating the remainder of the scar.
In Florida, Steven Weiner, MD is a Fraxel re:pair expert.
Good luck and be well.