Previously we studied lambda-integration paths for the calculation of "exact" surface and interfacial free energies that were limited to simulation methods where atomic interactions can be scaled using a multiplicative parameter lambda, as is the case for analytical empirical potentials. Here we develop new reversible paths and associated lambda-integration methodology to find exact surface and interfacial free energies of solids, that could potentially be used in conjunction with any intermolecular potential function and/or methods such as ab initio simulations, where one cannot trivially scale and sum the slab interactions as is done with "simple" classical intermolecular potentials. As a first step we test our paths and methodology on the (100), (110), and (111) faces of alpha-iron using embedded atom method interactions. We find accurate agreement with our previous surface free energy calculations for all faces, including the highly disordered (111) face.