Excel import is a convenience functionality if you want to have rapid diagram creation and all you have and all you know is spreadsheets. For roundtripping, the GraphML file format is much better suited than spreadsheets plus the whole Excel import procedure.
So, no, spreadsheet export is not supported.
With some fiddling, though, it seems possible to save to TGF file format, then transform the TGF to a .csv using a text editor with decent search-and-replace support.