I've done this a few times when I see that the title that gets recorded in the message board looks really bad or incomplete.
For example:
Sonic Riders ZG Zero G
ravity
There are various ways to go about it. If you use usb loader gx you can skip modifying the game data and use the cached banner on the sd/usb, and ULGX will use that for writing the message board info.
I find using a hex editor the fastest way, you may try other programs like u8tool or customizemii but both will require that you extract the banner first.