Requirements change management is one of the most complex and difficult problems to deal with in requirements elicitation and tracking. It is generally not understood how a specific change propagates through the specification and into implementation. In this paper, we propose to capture requirements changes as a series of atomic specification changes, and utilize state machines to model and manage those changes. We give a comprehensive treatment of state machine modifications with global impact, and propose twelve algorithms for managing all possible atomic requirements changes to a sequence-based specification. Finally, we demonstrate how to apply the proposed theory with a safe controller example.