Map from the old version will open: the game will update it when you log in. You can't get it back, so make a copy before doing so.
Map from a newer version You don't have to open the old one. The game will warn: "This world is preserved in the version ... and can be damaged by downloading this version!", and moving the world to the old version directly calls the game unsupported: "The transfer of the world to an old version is not supported." Put the version to which the map is made — usually the author indicates it.