A critical dimension in the handling of change in computer-based systems for cooperative work is whether mechanisms for change should be explicitly embedded into systems, or whether change should be handled in a global and uniform manner, for instance by a process of editing and recompiling programs or scripts on the fly. We argue that to reflect the structure of organisations, powers of change must be local, structured, and dynamic. Thus a global and uniform handling of change is in general insufficient. We propose a formal basis for the description of dynamically modifiable objects, and explore its applicability in the field of CSCW by exposing it to three examples of increasing complexity: A system for dynamic communication channel creation; an adaptable conversation manager; and a rudimentary, yet quite general, awareness model.