Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Up Vector
MG_POLY_UPVECTORParameter: Distribution
MG_POLY_MODE_Parameter: Selection
MG_POLY_SELECTIONParameter: Enable
MG_POLY_SELECTION_ACTIVEParameter: Restrict to Selection
MG_POLY_LIVE_RESTRICTParameter: Enable Scaling
MG_POLY_SCALEONPOLYParameter: Scale
MG_POLY_SCALEONPOLY_AMOUNTParameter: Scale Spline
MG_POLY_SCALEONPOLY_SPLINE