I think it would be appropriate to introduce a directory parallel to CROSSWORDS_DIR. Theoretically CROSSWORDS_DIR would also be suitable, as long as I don't name my state file with ".puz" at the end, but I don't want to trigger the CROSSWORDS_DIR=>database sync when writing my state.

Would it be okay to integrate the creation/maintenance of that directory into WordsWithCrossesApplication (so it is usable for other downloaders too, should they need it)?