Both business processes and business rules are changing over time. In addition, when business process models try to capture all details, they are complex and need to deal with variability according to context. Manual adaptation of process models takes time and is error-prone. The authors address these issues through explicit separation of process models (represented in BPMN) and specifications of business rules (represented as model transformation rules based on BPMN). Applying such rules as model transformations to a model of a reference process (at design-time) leads to models of either refined or new models of business processes.