[Powder]

The launcher DOES work using different named .exe (copies), but since there is only one ffxiv.cfg per installation folder, there is no way other than to have separate installs of the game to accomplish what you ask, or you would have to edit the FFXIV.cfg manually before running a new client for different settings, since when you close FFXIV that install will save the current settings to that same file again and overwrite them.

You could just copy the desired settings you want, save them, run the game, copy over different settings, save them again, then run the game.. Not automated but it should work