If I could +rep I totally would. I tried to make my SSS tutorials (for previous versions of the code) clean and easy to read, but this 1-up them on counts.
Just three things of note:
1) the fourth section actually controls the stages' positions on the custom random screen...moving icon/stage combinations around will change what stages can be picked on the random select. For instance, say you wanted to replace Bridge of Eldin with your first custom stage on the random select, you'd find BoE's stage/icon combination (330A) and do the same with the first custom stage's (4001) and simply swap their positions. BoE's picture doesnt change, but now any time it would be selected on random, your first custom stage will be selected instead.
2) The four digits FFFF that
MUST stay unchanged? Kinda, but not quite. In the original code, this section had to read '0064', the Menu's icon to make sure that it showed up on the My Music screen. With the v2 revision, this functionality was taken over by the unchanging portion of the code, and section 0x29 of the index (ie, the section we're talking about) became nothing more than a placeholder. The digits present in that section of the code don't matter, because, effectively, they're automatically overwritten. You could put 0101, or 1D17, or 5DB0, or whatever the heck you want, but it doesnt mean anything. Of course, failing to remember that that section gets overwritten will mean you lose a stage from your index, and that's never a good thing. So, is it imperative that that section be written FFFF? No. Is it dead space that you have to remember to skip? Yes.
Incidentally, in relation to point 1, all stages before the dead space are present on the random select, while none of the stages after it are. Sadly, I don't think trying to move the dead space around will do anything other than freeze your game at SSS loading
3) I don't think the end line E0000000 80008000 is supposed to be added. PW doesnt have it in the op and it isnt present in previous versions of the code. I havent checked, so i may be wrong.
For more info/my old tutorials, see:
v1:
http://www.smashboards.com/showthread.php?p=7897846#post7897846
v2 (unfinished, see post 17 for download):
http://www.smashboards.com/showthread.php?p=9008763#post9008763