Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Original Spline
SPLINEDEFORMEROBJECT_ORIGINAL_SPLINE
Parameter: Modifying Spline
SPLINEDEFORMEROBJECT_MODIFY_SPLINE
Parameter: B-Spline Approximation
SPLINEDEFORMEROBJECT_B_APPROX
Parameter: Radius
SPLINEDEFORMEROBJECT_RADIUS
Parameter: Use Length
SPLINEDEFORMEROBJECT_USE_LENGTH
Parameter: Full Polygons
SPLINEDEFORMEROBJECT_USE_POLYS
Parameter: Shape
SPLINEDEFORMEROBJECT_SPLINECONTROL