System and method having load control for isothermal expansion in turbine stage of gas turbine engine

A method includes routing a combustion gas through a turbine stage along a combustion gas path disposed between a turbine shaft and a turbine casing of a gas turbine, wherein the turbine shaft is disposed along a rotational axis, the turbine casing is disposed circumferentially about the turbine shaft, and the turbine stage includes a plurality of turbine vanes disposed upstream from a plurality of turbine blades. The method includes controlling an axial range of different axial positions of combustion within a turbine stage expansion of the turbine stage to reduce temperature variations over the turbine stage expansion via an isothermal expansion system coupled to the turbine stage in response to a change in a load on the gas turbine.