There is a crazy easy way to change your Nickname and birthday and favorite color on the DS Profile using a DS game.
The issue is that is follows the rules of DS so it's not at all useful (except that your DS Profile name can be different from the 3DS profile and you can get in like 10 DS Symbols, Hirogana, and Katakana, because the DS keyboard is superior to the 3DS one).
It's not hijack-able though.
Smealum used Bandai-O to change some stuff. I'm guessing he did some rom hacking, but I never really looked into it (because I'm running 6.0+ and I'm a noob).
Though editing it yourself isn't exactly easy. This post should help:
http://devkitpro.org/viewtopic.php?f=6&t=7793
This should get you somewhere until someone better can talk.