HELP: Seeking Sprite Update Mod

There are no people that release solely a sprite mod of the original game. You could however replace the number of sprite you want with FF3usME. I've compiled most of the spritesheets here. We also have a good base tutorial for sprites available here. Sections 4 and 6 are the ones that should interest you. In your case if you only want sprite swaps, you have to watch for custom palettes. There are roughly 6 palettes shared among 14 characters, Guests and all NPCs. Try sticking to sprites that use an original palette, but the spritesheets have not this specified in the compilation unless the info is in the thread of the said sprite.