Integrated mixed crop-livestock farming systems help improve farm sustainability by securing agricultural incomes through the diversification of productions and by enhancing farm autonomy regarding agricultural inputs. Based on interactions between crop and livestock productions within farms, such systems are complex to manage and to model. A one-to-one support methodology was developed to help farmers in their strategic thinking regarding the future of their farms in a redesign perspective. This methodology includes a three-step scenario process and is based on a spreadsheet simulation tool called CLIFS (Crop LIvestock Farm Simulator). CLIFS makes it possible to build scenarios of the evolution of a farm and assess them ex-ante by calculating several balances at the farm level (staple food, forage, manure) and their effects on the farm's economic results. The support process has been tested in several African and South American contexts and with French suckling cattle farms. The diversity of production contexts and issues addressed during the design process led to the development of a generic tool that can be applied easily to a large range of situations. A detailed description of the approach and the tool, with an illustration based on a Malagasy dairy farm, are presented here. Farmers appreciate the support process because it addresses their own questions within the context of their own farms. The process must now be transferred to advisory structures to assess its relevance in a professional context.