We have done that already for our PC translation. We are porting it to PSX now so we need to be able to change the PSX version too
EDIT:
CHOCOBO.DAT is the same for NTSC and PAL-E versions
First file is LZS compressed. The size of it is the first 4 bytes of the file + 4. It ends at 0x0004C063
-GFX Automatic/Manual Sequence, Long race: from 0x04C800 to 0x055026 (1024x256, 4bpp)
palettes for Automatic starts at 0x10100 (65792, 32 bytes)
Manual starts at 0x10300 (66304, 32 bytes)
-GFX Automatic/Manual Sequence, Short race: from 0xx97000 to 0x09D6C9 (1024x256, 4bpp)
-GFX Race A CLASS, etc.: starts at 0x0C2000 ends at 0x0CF8ED (1536x256, 4bpp)
-GFX Race B Class: starts at 0x0D0000 ends at 0x0E2860 (1536x256, 4bpp)
-GFX Race C Class: starts at 0x0E3000 ends at 0x10409B (1536x256, 4bpp)
-GFX Race S Class: starts at 0x104800 ends at 0x119D59 (1536x256, 4bpp)
We where able to modify the graphics and luckily the new compressed files where smaller but we are still missing the index which might be inside CHOCOBO.BIN. If somebody is willing to explore it i'll appreciate it