Globally distributed software enhancement necessitates joint efforts of workforces across various organizations, which constitutes a multifaceted social network. Here, we propose a novel modeling framework to optimally assign the workforce to software development projects considering both short and long-term benefits of the organization. The proposed framework is composed of the evaluation module, an agent-based simulation model representing the considered social network; and the assignment module, a multi-objective optimization model. The Decision Evolution Procedure of the evaluation module first calculates the position values between each pair of available workforce. Using these position values, the Extended Regular Equivalence Evaluation algorithm of the evaluation module then computes the regular and structural equivalence values between each pair of workforce. Finally, the assignment module selects the optimal workforce mix maximizing both the short (productivity) and long-term performance (robustness) of the organization. The proposed framework is demonstrated with the software enhancement process in Kuali organizational network.