A system includes an HRSG that includes a plurality of heat exchanger section fluidly coupled to each other. The plurality of heat exchanger sections comprises at least one economizer, at least one evaporator, at least one reheater, and at least one superheater. In addition, the HRSG includes an additional heat exchanger section coupled to two different heat exchanger sections of the plurality of heat exchanger sections. Further, the HRSG includes a controller programmed to selectively fluidly couple the additional heat exchanger section to one of the two different heat exchanger sections to alter a heat duty for the selected heat exchanger section fluidly coupled to the additional heat exchanger.