A key factor for the successful implementation of mass customization is joint product-process optimization. This paper proposes a linear programming model that jointly optimizes product configuration and process planning in a reconfigurable manufacturing system (RMS) to minimize manufacturing costs while ensuring individual customer requirements (CR) satisfaction. The impact of the initial RMS configuration and changes in CRs on the total cost is investigated. The results show that for a given set of CR, different product variants can appear like the optimal solution, and the total cost can vary up to 30%, confirming the benefits of joint product-process optimization.