Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Optimize Hierarchy
VRML2IMPORTFILTER_OPTIMIZEParameter: Optimize Structure
VRML2IMPORTFILTER_OPTIMIZESTRUCTUREParameter: Import Normals
VRML2IMPORTFILTER_USENORMALS