Wait..

[Custom]

Go here
http://www.guitarhero.com/accounts;search

Look up NS Custom13

Both are me. One is my game, one is my account there. Is there any way I can link both so I have 105 groupies instead of 42/63? >>

[sonicdude164]

Ask an admin there

[Custom]

Ask an admin there

Do you know of one's s/n?

[sonicdude164]

Sorry, I have no clue

[Light]

Go to Nintendo Wi-fi connection in your game (GHIII), go to the www.guitarhero.com selection, and there should be a code in big, white letters/numbers. Then actually go to www.guitarhero.com, log in, select "link account" from the pull down menu in the upper right hand corner, and go to the bottom and put in the code.

I think that's how you do it.