"After the preparation of the operational Safety Case any ammendments to the deployment of the system should be examined against the assumptions and objectives contained in the safety case" Ministery of Defence Safety Standard 00-55, Section 4.7.1.
T. Kelly and J. McDermid, A Systematic Approach to Safety Case Maintenance. In M. Felici, K. Kanoun and A. Pasquini (eds), Computer Safety, Reliability and Security, Springer Verlag Lecture Notes in Computer Science 1698, 1999.