In the main within_gameplay_Menu, you can always save the map itself by clicking the provided button in the Saves/Loads section. This map will then be ready for some editing by WorldBuilder if you load it from the ..\MyGames\Civ5\.. folder. Afterwards, it can only be re-used for some new games, though.
But there's no actual direct stock-official "savegame" editor (that would certainly be equal to purely cheating in fact) -- yet!