Livestock systems are and will increasingly be impacted by climate change primarily because the feed supply produced on the farm (pastures, forage crops) depends greatly on the climatic conditions experienced. To adapt grassland-based livestock systems to climate change, some transformational redesign of the farming system may be required. Redesign is basically a matter of reconfiguring land-use for feed production and management practices set up to cope with weather variability. We present a participatory method to design systems adapted to new conditions. It is based on a pre-existing game-like platform (Forage Rummy) in which various year-round forage production and animal feeding requirements have to be assembled by participants with the support of a computerised support system. The weather scenario considered is conveyed by dedicated intermediary objects (e.g. herbage growth chart, rainfall chart) for a climatic year that is fully revealed before the design process starts. The solutions developed are then evaluated according to criteria of biophysical performance, organisational feasibility, and feeding shortage risks. The method consists of a sequence of three workshops (W) for which Forage Rummy was adapted. It keeps the complexity of the design problem manageable by progressively introducing the difficulties faced. W1 aims to produce a configuration that satisfies an average weather scenario of the future. W2 refines or possibly revises the previous configuration by considering between-year variability. W3 explicitly takes uncertainty about the weather into account. Unlike W1-2, in which entire weather scenarios are shown at the beginning, weather is only revealed month by month in W3. Experimental results of the use of the method with farmers are analysed, and further enhancements of the method are outlined.