If we imagine that excess water from Wyoming is used to grow crops in California, it seems reasonable to assume that it would be less moisture/precipitation for

If we imagine that excess water from Wyoming is used to grow crops in California, it seems reasonable to assume that it would be less moisture/precipitation for Nebraska. But if it is used to grow wheat in Colorado (because the obligations to lower-basin states need to be met regardless and the increased moisture allows more diversions across the continental divide), then it probably ends up evaporating anyway or else in the Platte River. It wouldn't be stealing moisture from Nebraska, they might actually benefit from it. Geo-engineering might not have a free lunch, but it also isn't a zero-sum game.