Distributed software systems are built by composing independent and autonomous peers with cross-organisational interaction and no centralised control. These peers can be administrated and executed by geographically distributed and autonomous companies. In a top-down design of distributed software systems, the peers’ interaction is often described by a global specification called Conversation Protocol (CP) and one have to check its realisability i.e., whether there exists a set of peers implementing this CP. In dynamic environments, CP needs to be updated wrt. new environment changes and end-user interaction requirements. This paper tackles CP evolution such that its realisability must be preserved. We define some evolution patterns and prove that they ensure realisability. We also show how our proposal can be supported by existing methods and tools based on refinement and theorem proving, using the event-B language and RODIN development tools.