You'll have to earn both a title and an icon; You can't just set them as the default.
Titles are easy to earn. The fasted is to complete a single character-specific challenge. Other easy ones include one for playing a single online match (win or lose) and for reaching the third rank of timed or survival challenge. Note that nearly every icon will give you a title as well.
Icons are harder. There's one for winning a single online battle. Another is for 30 perfect rounds (online or off), or dizzying an online opponent. Most of the rest require clearing all challenges Normal and hard of a single type or for a single character. Good luck with that.
Once you have one of each, go to the main menu and hit RB. Achievement should pop as soon as you set each one.
If you have any questions, further advice for this game, or ways to improve this solution, please post a comment. Suggestions for other easy Titles and Icons would be appreciated.