Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Transform
MGEXTRUDEDEFORMER_MODEParameter: Extrusion Steps
MGEXTRUDEDEFORMER_STEPSParameter: Polygon Selection
MGEXTRUDEDEFORMER_SELECTIONParameter: Sweep Spline
MGEXTRUDEDEFORMER_SPLINE