Okay, straight ports from PAL:

Allow overriding player characters [link]
041CD914 60000000
Use together with the player list - activating this code will enable overriding player characters

Allow overriding CPU characters [link]
041CDE70 60000000
Use together with the player list - activating this code will enable overriding CPU characters

Player list [link]
06553454 00000040
XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX
The game handles a list of 16 possible characters. This is the list of chars in the events - in the 4 by 4 events (swimming for example) all 16 are required, otherwise just 8 or 4
Please note that using chars different to the regular 16 chars might freeze the game! Activating both overriders will render the character selection completely useless! Using one character multiple time is absolutely ALLOWED!
The first XXXXXXXX is player 1, then player 2 and so on!
XXXXXXXX may be:
00000000 Mario
00000001 Luigi
00000002 Peach
00000003 Daisy
00000004 Yoshi
00000005 Birdo
00000006 Bowser
00000007 Donkey Kong
00000008 Wario
00000009 Waluigi
0000000A Sonic
0000000B Tails
0000000C Knuckles
0000000D Amy
0000000E Shadow
0000000F Eggman
00000010 Silver
00000011 Vector
00000012 Jet
00000013 Blaze
00000014 Shy Guy
00000015 Toad
00000016 Lakito
00000017 Charmy
00000018 Espio
00000019 Cream
0000001A Boo
0000001B Bullet Bill
0000001C Goomba
0000001D Heroes Enemy 1
0000001E Heroes Enemy 2
0000001F SA1 Monkey
00000020 Big
00000021..24 Mii

Size enable code [link]
C2217738 0000000A
3F208000 3B391000
3FE0B48B 3BFFA15C
83470070 83790000
2C1B0000 41820028
7C1AD800 40820018
C0390004 7C1FD000
40820018 D0340080
48000010 3B390008
4BFFFFD4 C0340080
60000000 00000000
Without this code size modifiers won't do a thing!