Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Subdivision X
BEZIEROBJECT_SUBRXParameter: Subdivision Y
BEZIEROBJECT_SUBRYParameter: Grid Points X
BEZIEROBJECT_SUBXParameter: Grid Points Y
BEZIEROBJECT_SUBYParameter: Closed X
BEZIEROBJECT_CLOSEXParameter: Closed Y
BEZIEROBJECT_CLOSEY