Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Circle Subdivision
DXFIMPORTFILTER_CIRCLESEGMENTS
Parameter: Connect
DXFIMPORTFILTER_LAYER
Parameter: Frozen Layers
DXFIMPORTFILTER_FROZEN
Parameter: 2D Elements
DXFIMPORTFILTER_ELEMENTS2D
Parameter: Align Normals
DXFIMPORTFILTER_ALIGN
Parameter: Triangulate Polygons
DXFIMPORTFILTER_TRIANGULATE