Incremental changes add new functionality and properties to software. They are the core of software evolution, maintenance, iterative development, agile development, and similar software processes. This paper presents a technique for unanticipated incremental software change and a case study. The technique uses programming concepts as the foundation, and contains steps of concept location, actualization, incorporation, and change propagation. The case study presents an unanticipated change in the open source software “Drawlets”.