We present a formal approach for partial transformation of scenario-based specifications. Scenarios are captured as sequence diagrams (SDs) and (partially) transformed into coloured Petri nets (CPNs). Partial transformation is of interest for local analysis, or within an incremental development approach where interaction specifications are built incrementally and combined with previous iteration models. In previous work we defined a strongly consistent trans- formation from SDs to CPNs. In this paper, we extend the approach for partial transformation whilst preserving the strongly consistent nature of the transformation.