Always Sonic:
0124EE6C
00000000

Always Shadow:
0124EE6C
00000001

Always Knuckles:
0124EE6C
00000004

Always Rouge:
0124EE6C
00000005

Always Tails:
0124EE6C
00000006

Always Eggman:
0124EE6C
00000007

With this code, you can modify which level loads on Stage Select:

0124EE64
000000??

Replace the ?? with one of the following

00 - TEST LEVEL
01 - *Crash*
02 - *Crash*
03 - Green Forest
04 - White Jungle
05 - Pumpkin Hill
06 - Sky Rail
07 - Aquatic Mine
08 - Security Hall
09 - Prison Lane
0A - Metal Harbor
0B - Iron Gate
0C - Weapons Bed
0D - City Escape
0E - Radical Highway
0F - 2 Player - Weapons Bed Area
10 - Wild Canyon
11 - Mission Street
12 - Dry Lagoon
13 - Boss: Sonic vs Shadow at Green Forest
14 - Boss: Tails vs Eggman at Weapons Bed
15 - Sand Ocean
16 - Crazy Gadget
17 - Hidden Base
18 - Eternal Engine
19 - Death Chamber
1A - Egg Quarters
1B - Lost Colony
1C - Pyramid Cave
1D - Boss: Tails vs Eggman at the Ark
1E - Final Rush
1F - Green Hill
20 - Meteor Herd
21 - Boss - Rouge vs. Knuckles at Meteor Herd
22 - Cannon's Core - Sonic
23 - Cannon's Core - Eggman
24 - Cannon's Core - Tails
25 - Cannon's Core - Rouge
26 - Cannon's Core - Knuckles
27 - 2 Player Battle - Mission Street
28 - Final Chase
29 - *Crash*
2A - Boss: Sonic vs Shadow at Ark Runway
2B - Cosmic Wall
2C - Mad Space
2D - *Crash*
2E - *Crash*
2F - Mini Stage - Pyramid Race
30 - 2 Player - Sand Ocean
31 - Mini Stage - Pool Quest
32 - Mini Stage - Planet Quest
33 - Mini Stage - Deck Race
34 - Mini Stage - Downtown Race
35 - 2 Player - Ark
36 - Mini Stage - Grind Race *Crash*
37 - 2 Player - Lost Colony
38 - 2 Player - Ark
39 - 2 Player - Metal Harbor
3A - 2 Player(?) - GUN
3B - 2 Player - Death Chamber
3C - Boss - Big Foot
3D - Boss - Hot Shot
3E - Boss - Flying Dog
3F - Boss - King Boom Boo
40 - Boss - Egg Golem
41 - Boss - Biolizard
42 - Boss - FinalHazard
46 - Route 101 (And Route 280...)
47 - Kart Racing
5A - Chao World