Are the grass instances just instances in a Hierarchical Instanced Static Mesh Component or are they stored in another special way? If they are just instances, it would be enough to set the instances which should disappear to a scale of 0, then the grass would not have to get “regenerated” since all instances stay where they are. I don’t think there is a way to get the grass hit by a trace to get the instance index in a specific area, but if we could access the Component the grass is stored in then we could just loop through all instances and compare the instance location with the location where we want to remove the grass. A waste of performance, but it would be a nice workaround until Epic introduces an official solution.