Given the frequent failure of internationally established reconciliation tools, traditional conflict resolution mechanisms are increasingly integrated into transitional justice programmes in order to locally root peace. However, traditional justice mechanisms can be highly ambivalent; they can be, at the same time, inclusive and exclusionary, thus promoting peace or triggering new conflict. In Eastern Indonesia, where the author has conducted extensive field research, local actors took up these challenges and try to adapt local justice mechanisms so that they can cope with mass violence and the reintegration of conflict parties and society. Social engineering is promoted as one solution to the problem. This article looks at various conceptualisations and implications of social engineering – from a top-down authoritarian to a bottom-up participatory approach – and discusses how far this controversial concept and the deliberate adaption of local traditions to new challenges should be taken into account in future peace research and work as well as in anthropological debates.