It was found recently that multiferroic Pb(Fe1/2Nb1/2)O3 (PFN) has a complex crystal structure containing nanoscale regions of Fe ions segregated into chemical clusters. This unusual property may have exciting applications, for instance, in magnetic, electric, or magnetoelectric devices, and it definitely has a fundamental significance. However, this challenge will be unclaimed until one can find the way how to control this property. In the present study, we investigate the possibility of using an epitaxial strain for these purposes. We have performed first-principles calculations of the energies of different chemical configurations of PFN for a wide range of the misfit strains. We found that the misfit strain does influence the energy, magnetic moments, crystal shape, ferroelectric, and even antiferroelectric polarization of PFN, due to a different response to the strain of different chemical configurations. This makes the epitaxial strain one of the most valuable candidates to control the chemical clustering in PFN.