The VG Resource

(I'm hoping that this is the right section. Tried to narrow it down as much as I could)

I was wondering whether it's possible to modify two things in a ROM in Visual Boy Advance. (Using other programs if needed)

Is it possible to modify palettes and sprites? Like exporting a palette or spritesheet, modifying it in the appropriate program and then re importing it into the ROM.

(I've already checked the tutorial page)

People take a large part in modifying Pokemon Roms.

Granted people crafted tools to be able to do so. I think
you would be able to do it on other roms as well though.

u need to to whahackpokemon.com, click english and check it out...it sort of helped me but i hope it does better for you