Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Object
OSHAPE_OBJECTParameter: Bounding Radius
OSHAPE_RADIUSParameter: Render Instance
OSHAPE_RENDERINSTANCEParameter: On
IN_OSHAPE_ONParameter: Animation Time
IN_OSHAPE_ATIME