Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Circle Subdivision
DXFIMPORTFILTER_CIRCLESEGMENTSParameter: Connect
DXFIMPORTFILTER_LAYERParameter: Frozen Layers
DXFIMPORTFILTER_FROZENParameter: 2D Elements
DXFIMPORTFILTER_ELEMENTS2DParameter: Align Normals
DXFIMPORTFILTER_ALIGNParameter: Triangulate Polygons
DXFIMPORTFILTER_TRIANGULATE