This paper explores constitutions of a co-design approach for releasing the transformative potentials of design, through a sustainable service design project called BeChange. Some of the more recent design approaches are means to address a wider range of issues and areas than previously thought of in design. In an innovative project, there are no real users before solutions have been launched, so how does one approach transformative co-design, and who should one co-create with? There is still scarce knowledge, particulars, and examples of how such transformative co-design projects are approached, the incentives for such deeds, and the challenges involved, that can form principles for transformative co-design. Drawing on literature reviews of transformation, participation and service design, and through outlining BeChange, the objective is to explore constitutions of such practices. The overall vision was of creating sustainable lifestyle changes, and the mission was of co-designing a digital service concept. The approach involved co-design sprints, to better understand behavioural changes, authentic sustainability, and user experiences through prototyping. With respect to preceding design research, this paper provides insights of co-design practices with a focus on transformation, in regard to the wicked problems of exploring behaviour changes and co-creating future services with prospective users.