Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Subdivisions
CNURBS_SUB
Parameter: Factor
CNURBS_FAK
Parameter: Limit
CNURBS_LIMIT
Parameter: Thickness
CNURBS_DOUBLE
Parameter: Bulging
CNURBS_PARALLEL