modding tools for gba games

hi im looking for rom tools that can alter a gba games layout as i want to make a new version of castlevania circle of the moon where you play as nathan graves rival and not nathan
if anyoen can help please let me know thanks

Have a look at this list:http://www.romhacking.net/?category=&Platform=10&game=&author=&os=&level=&perpage=50&page=utilities&utilsearch=Go&title=&desc=

thank you very much
now my golden sun hack can begin new story too well partallyPost Merge: [time]1315611890[/time]
and my castlevainia one too