Reconfiguration is one of the most important capabilities of optical networks. This task is performed by operators to re-optimize network resource utilization. Multicast applications such as videoconference online learning, etc., emerge rapidly and cause an increase in bandwidth demand. A multicast connection in an optical network is provided by a light-tree. Due to physical link failures, light-trees are protected by backup paths. Thus, our study focuses on the reconfiguration of a protected light-tree. The reconfiguration problem studied here is to migrate rapidly an optical flow from an old light-tree to a new light-tree without service disruption. To solve this problem, we propose a mechanism based on dependencies graphs. This method establishes simultaneously groups of the final light-tree branches by using shared backup paths spectrum resources. The numerical results show that our approach avoids flow interruptions and reduce significantly the number of steps required to achieve the reconfiguration process more than existing methods.