Hello!

Yes, using Special Characters for the in-game name is possible. While using a Rename Card, type your desired name somewhere (like Notepad or Wordpad) and copy-paste it in the text box in-game. But I would also like to warn you about doing that, some Special Characters are not recognized by the game and by using that Special Characters can make your character being not able to messaged by others nor be invited in a team, so be careful of doing it.