So, you can save the installation by doing this.

1. Install the Launcher from Steam
2. Go to your FF XIV installation folder (The full one) and make a copy of a file called "gameversion", move it to your desktop if you want or leave it there.
3. Cut everything from the folder and paste it to the Steam's installation folder. (You can open it by right-clicking on FF XIV at the Steam library, properties, local game files and open location or going to the Steam's installation folder, steamapps, common, Final Fantasy XIV Online)
4. Paste, it'll ask you if you want to replace a few files, say no.
5. Take the file we copied, gameversion, and overwrite the Steam folder's one.
6. Open up your launcher, voila.

Its a bit tedious if you're a bit slow with things like this, but you don't have to reinstall whatsoever. I think HUD stuff and other info is in "My Documents" folder inside the My Games > Final Fantasy XIV, don't quote me on that.