We measured the pressure-induced shift and broadening of spectral holes for 14 different impurity sites in a polycrystalline solid solution of chlorin (17,18-dihydro-21H,23H-porphine) in benzophenone. In addition, we investigated the glassy phase of the same system in a frequency range which covered the entire inhomogeneously broadened band. The temperature range of the experiments was between 1.5 and 4.2 K. Pressure levels up to 10 MPa were applied. In the glassy phase, we observed a linear frequency dependence of the shift per pressure. However, in the crystalline phase, the general trend of the data clearly indicated a nonlinear frequency dependence. Yet, the individual sites, especially those with lower frequencies, showed a kind of stochastic scattering around the general trend behavior. Tle results were interpreted within the frame of existing models. The experiments demonstrate that matrix isolation combined with hole burning spectroscopy of large molecular impurities in polymorphic host materials under varying pressure conditions is a useful technique for determining molecular as well as bulk parameters, for examining problems of microelasticity and microplasticity, and for investigating the fundamental differences between glasses and crystals.