A tubular centralizer is secured to the tubular for run in. The profile for run in is small so that damage to the centralizer is minimized during run in. When the string is in position the centralizer is actuated to change shape or volume to engage the surrounding borehole to centralize the tubular for subsequent operations such as cementing or in the case of screens for gravel packing. The centralizer can be a shape memory material that is initially compressed at above its transition temperature to hold the smaller shape. At the desired location after run in it is brought above the transition temperature and changes back to the original shape or volume to centralize the tubular string. The structure can be spaced ring segments or a cohesive ring structure with an undulating profile or radiating blades to create flow spaces in the annulus where it is deployed for flow of a sealing material or gravel, for example.