SSS theorem or side-side-side triangle congruent theorem state that each side of one triangle must be congruent to the opposite side of another triangle. It means they same measurements. So, when triangle DEF is congruent to triangle D'E'F by SSS theorem, the only transformation that can be done is the measurements of one side of D'E'F is move to other sides as well as the next two sides, but it would have remained that all sides are having the same length to each side of DEF.