Changing Tiles...

Well, I just search and look. After awhile you'll start to remember whereabouts everything is located, weapons, map tiles, spell graphics, all the sprites. I'm sure that somewhere the offsets are listed for everything, maybe somewhere like in Cless's FFVI Romhacking Guide, or just a ROM map of FFVI, but searching for the tiles you want to change is pretty easy.

It also really helps if you're having trouble locating the tile due to the crazy looking colors of YY-CHR, you can load an emulator save state that has the current palette in it, and it will then show the right color. This is mighty useful for things like spells and weapon, and I'm sure tiles as well.