Hex Address

1. Big "2" is art. Decompress the title screen art and edit.

2. Most offsets can be found in Nemesis' guide here: Nemesis' Homepage

3. No 2 roms have exactly the same offsets, unless they are the same game. The only exception to this is the rom header, which of course is always at 0x000000 :D

 

Actually, I think that Sonic 2 and Sonic 3 have a level select in the same location.
Supposedly, you can switch carts with the Sonic 2 cheat on, reset, and the level select will be available with Sonic 3.
This is allegedly why the art is the same for the Sonic 3 level select.

 

I don't really see how it can damage it much.
SUBLIMINAL MESSAGE: CLEEN UP UR GRAMMARZ LOLDIE

 

For editing compresed art, I have a tutorial in E&RE - Archive. It shows you how to find and edit compressed art using the Sega Data Compressor. Find it here. I hope this helps

EDIT - aargh, there's an image in this topic which crashes IE!

 

Could mess up your saves in Sonic 3, but I think that's about it. Still, I've never tried it.

Download the SEGA data compressor. (Geez, what would we do without Magus?)

 

I did this several times, never damaged anything.