A System of System (SoS) is a synthesis of independent systems functioning together towards a common goal. They are characterized by their dynamic nature and evolvability during operation: addition, removal, and modification of component systems and functions. It is, therefore, important to characterize the tolerance of such systems to changes and failures. Most change propagation and failure analysis methods require some knowledge of failure and change probabilities, failure modes, and design parameters, which is difficult to obtain or unavailable to an SoS decision-maker, as component systems are independent in their management and operation. Consequently, this paper uses highlevel SoS functional models and network-based metrics to characterize SoSs functions and assess the functional change and failure of such systems. The proposed measures are deployed on an electric vehicle to grid-related service to show how it can aid an SoS decision-maker during the system's development and operation.