HOW TO DO
1. First you download ifunbox and the hack file.
2. Download the game from Appstore
3. Launch the game, when it asks you to log in or register just quit the game
4. In ifunbox go to Applications==>Yu-Gu-Oh!, you will have a few folders, just don't touch
5. Click on "Copy from mac/pc" and search for the hack ("Documents")
6. Quit ifunbox
7. Launch the game, register a new account
8. Done!
You can't use the hack for an actual account, the reason is that the server saves your account datas and synchronise them with your game every time you launch it. Well, there's may be a way to do this with your actual account but I didn't find it.
'Hope it will help.