Update the Normals and/or Tangents at VertexID of TargetMesh. Note that the specified vertex may have "split normals" or "split tangents", ie in the case of hard/crease normals, UV seams, and so on. In these situations, by default each of the unique normals/tangents at the vertex will be updated, but they will not be "merged", ie they will remain split. However if bMergeSplitValues=true, then the vertex will be "un-split", ie after the function call the vertex will have a single unique shared normal and/or tangents.