3. Now just to see if the image is correct, open up NTME, and then for the tileset, select the image you saved. Then go to Load Raw, and select the other file you saved. http://img20.imageshack.us/img20/1162/pic6s.png
Well, look! It's the Team Magma logo. That's what were going to modify.
4. Now here comes the hard part. Make a TileSet of the image you want to change the logo into. What I did, is make the logo, and then turn it into an 8x8 grid, and then delete all repeated tiles, and then put them into the image you saved.
And that's your final result! Additionally, you can use APE to change the palette too. You can also use this tutorial for almost anything you can find in unLZ with a TileSet and a raw file right after it.
HackMew - I used his hacked unLZ.gba
Larsie13 - For his tutorial on how to edit the worldmap
D-Trogh - I used NTME