This paper introduces a novel approach for improving the adaptability and scalability of modular assembly systems by integrating decentralized, agent-based control with state-based planning. Traditional assembly systems struggle with adapting to varying production demands due to their reliance on fixed, centralized workflows. Our proposed concept leverages state-based descriptions of assembly processes and a multi-agent system to enable real-time reconfiguration and dynamic process planning. This approach facilitates seamless adaptation to changes in production volume and product types, reduces installation times, and extends the operational life of assembly equipment. The results demonstrate improved flexibility and resilience compared to conventional methods, offering significant implications for future research and application in manufacturing environments, particularly in industries requiring rapid responsiveness to market shifts.