Determination of the removal function is an important step in magnetorheological finishing (MRF) of optical materials. However, the removal function is difficult to determine if a spot sample of the same material as that needing polish is unavailable, thus preventing establishment of an MRF process plan. A method to resolve this issue is proposed, wherein an MRF process plan for an item of a differing optical material is migrated. The theoretical basis for migration is investigated, and simulations reveal that narrow nonlinear regions of the source and target materials’ removal functions are a necessary condition for adequate convergence rate. The proposed method is experimentally verified by finishing a ZnS part with the process plan of a BK7 optical part of the same geometry, with a convergence rate of 45.7% after four iterations.