Bridge Correction patch

Changing just small things, you just decompress with Peer Sprite Viewer, edit with YY-CHR, and then recompress and reinsert with PSV. If you want to make more extensive changes to the battle backgrounds, they'll likely be a different size when recompressed with Peer Sprite Viewer. If they're too big, you'll overwrite data and corrupt other battle backgrounds.

I'm not sure if PSV shows you the size of the compressed data before you recompress and reinsert. So when I wanted to change a battle background, I just recompressed and reinserted it to an area of empty space in the ROM, then used my hex editor (WindHex) to export a binary file of that data. Knowing the size, I shifted the background data and imported my binary blob, then changed the pointer table to the proper new values.

I don't know the address of the pointer table offhand, but that and more info is in Dr. Meat's thread about FFVI Relocalization Project. He imported the FF6j backgrounds to FF3us and documented his process nicely.