The main thread you're going to want to read is the
DOL Mod Topic here in the
Melee Workshop. There's a ton of info in the whole thread so I'd suggest you read at least the first few pages.
You have a couple options for how you want the hack to be put in.
The easiest route is to insert an
already modified .dol file with the Debug menu hack (and a ton of other hacks) into your ISO along with the
Visual Mod using the program
GC-Tool. There may be some hacks in the already modified .dol that you don't desire so I'd suggest editing the .dol file yourself for specific hacks you may want.
If you want to do it manually you'll need to open up the .dol file from your Melee ISO (extracted from the ISO using GC-Tool) with any Hex Editor (such as
HxD or Hex Workshop), find the address of the mod and change the values to the modded ones. Here's a quote from the DOL Mod Topic about this.
Debug Menu replaces Tournament Mode
-Selecting Tournament Melee in the main menu takes you to the Debug Menu instead
-Selecting Single Button Mode takes you to the Tournament Melee mode instead
[Magus, donny2112, SypherPhoenix] - Concomitant Graphical Mod Here
Version ── DOL Offset ────── Hex to Replace ────────── ASM Code
1.00 ────── 0x228F20 ──── 3800001B -> 38000006 ──── (li r0,27 -> li r0,6)
─────────── 0x227F2C ──── 3800002C -> 3800001B ──── (li r0,44 -> li r0,27)
1.01 ────── 0x229A90 ──── 3800001B -> 38000006 ──── (li r0,27 -> li r0,6)
─────────── 0x228A9C ──── 3800002C -> 3800001B ──── (li r0,44 -> li r0,27)
1.02────── 0x22A218 ──── 3800001B -> 38000006 ──── (li r0,27 -> li r0,6)
─────────── 0x229224 ──── 3800002C -> 3800001B ──── (li r0,44 -> li r0,27)
PAL ─────── 0x22C084 ──── 3800001E -> 38000006 ──── (li r0,30 -> li r0,6)
─────────── 0x22B08C ──── 3800002F -> 3800001E ──── (li r0,74 -> li r0,30)
It may be a little hard to understand at first but all this really says is go to Address
0x229A90 and change it's value from 3800001B to 38000006. Same thing for the Address
0x228A9. The ASM Code isn't important unless you know what you're doing with it.
If this doesn't make a whole lot of sense please read the DOL Mod Topic and you'll gain more understanding about how the whole hacking process works.