It is possible to recut diamonds. It would have to be examined to determine that possibility. The amount of weight lost would probably be determined by the characteristics of the diamond (inclusions, stress, current proportions) and the level of cut quality you desire. The cost will likely depend upon who recuts the stone. For the ultimate in cut, there's EightStar which will cost more than getting an average cutter to cut an average stone or a middle of the road cutter to cut a so-called "ideal" or hearts and arrows-type cut.Does this help?