Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: N-gons
MDATA_MAKESELECT_NGONSParameter: Quads
MDATA_MAKESELECT_QUADSParameter: Tris
MDATA_MAKESELECT_TRISParameter: State
MDATA_MAKESELECT_STATEParameter: Select
MDATA_MAKESELECT_SELECT