Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Original Spline
SPLINEDEFORMEROBJECT_ORIGINAL_SPLINEParameter: Modifying Spline
SPLINEDEFORMEROBJECT_MODIFY_SPLINEParameter: B-Spline Approximation
SPLINEDEFORMEROBJECT_B_APPROXParameter: Radius
SPLINEDEFORMEROBJECT_RADIUSParameter: Use Length
SPLINEDEFORMEROBJECT_USE_LENGTHParameter: Full Polygons
SPLINEDEFORMEROBJECT_USE_POLYSParameter: Shape
SPLINEDEFORMEROBJECT_SPLINECONTROL