This descriptive, longitudinal case study report upon the experiences from a medium-sized packaged software product supplier in their improvisation-like transition from a plan based process to Evo-an agile, evolutionary process. We focus on the organizational implications for the supplier including customer collaboration, process control and psychological comfort. We introduce the concept "process fragility" in our discussion of critical process attributes and explain why this attribute should be taken into consideration. Our findings are primarily based on qualitative analysis of successive interviews with developers, product management and involved customers. Evolutionary product development improves stakeholder engagement and developer responsiveness over plan-based processes but requires cross-organizational discipline and involved management. Our findings may give important advice to other product companies considering evolutionary development practices.