The equivariant cohomology ring of a regular semisimple Hessenberg variety in type A is a free module over the equivariant cohomology ring of a point. When equipped with Tymoczko's dot action, it becomes a twisted representation of the symmetric group, and the character of this representation is given by the chromatic quasisymmetric function of an indifference graph. In this note, we use divided difference operators to decompose this representation as a direct sum of sub-representations in a way that categorifies the modular relation between chromatic quasisymmetric functions.