Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Strength
MDATA_FLATTEN_WEIGHT
Parameter: Mode
MDATA_FLATTEN_METHOD
Parameter: Axis
MDATA_FLATTEN_AXIS
Parameter: Use Axis Position
MDATA_FLATTEN_USEAXISPOSITION
Parameter: Position
MDATA_FLATTEN_PLANEPOSITION
Parameter: Individual Islands
MDATA_FLATTEN_INDIVIDUALISLANDS
Parameter: Outline Only
MDATA_FLATTEN_OUTLINEONLY