It’s hard to say without having a screenshot of the entire material graph, but if you are talking strictly about the LandscapeGrassOutput node, then no. Not that it is a limitation of the engine, which is also quite possible, as the Landscape functions of the SM5 shader can be very temperamental, but because that’s not what you’d want to change.
You’d want to change things like the textures used and other values assigned to inputs prior to the tool.
Correct, materials instances can change anything about the layer alpha that drives the placement of the grass but they cannot change what type of meshes are spawned currently.