In other words,
How do I change the music that plays in the credits?
In AMKGUI.exe, change:
38 Staff Roll.spc -> Change it by your song
39 The Yoshis Are Home.spc -> Change it by your song
40 Cast List.spc -> Change it by your song
Then click "Run" and that's it.
This is a 7-year-old thread whose author is inactive. It has served its purpose long ago, not to mention that AddmusicK didn't exist back when it was made.
Do not needlessly bump old threads, especially not ones which are this old.