System of systems (SoS) engineering is an emerging approach to deal with complex systems that have low or no control over their constituents. An SoS must adapt itself not only to the willingness of its constituents to participate or disengage, but also to evolving needs. As reconfiguration is a routine task, the SoS architect needs specific assistance, especially to easily identify reusable solution principles and to track her/his decisions in the design of reconfiguration. To address these issues, we propose to introduce the concept of reconfiguration pattern based on prior design and architectural patterns. These patterns constitute well-documented, principled and adaptable solution building blocks. We illustrate our approach with one reconfiguration pattern applied on an example based on the French communication system for emergency services.