Business processes are changing over time, e.g., due to new or changed legal regulations. Complex processes are susceptible to change, since they capture much detail and/or deal with variability according to context. Manual adaptation of process models according to such changes takes time and is error-prone. In order to address these issues, primarily complexity, we propose to model high-level reference processes with less detail than the fully-fledged processes. The missing details are captured in additional business rules that operationalize how an organization performs miscellaneous tasks. Their application to a high-level reference process leads to its refinement. Technically, we propose explicit separation of process models (represented in BPMN) and specifications of business rules (represented as model-transformation rules based on the BPMN 2.0 metamodel). Applying such rules as model transformations to process models (at design-time) leads to models of either refined or adjusted models of business processes. In this way, even without any extension of the BPMN 2.0 standard, these model adaptations can handle the required changes of business processes.