OK what i found is the start of the .bin is the ToC (Table of Contents) which tells the game where files in the .bin are, there are basically 2 methods to deal with this.
Method 1 (easy way) - Use a hex editor to manually overwrite the old files with the new ones but the new ones MUST BE SMALLER OR THE SAME SIZE then the old ones (if they are smaller i recommend padding the file to the same size as the original), they can NOT BE BIGGER THEN THE ORIGINAL files, this is the easiest way since you can leave the ToC as is and also makes it easier to reinsert into the game since the opening.bin will be the same size.
Method 2 (hard way) - Completely remake the .bin using what was said above (a file joiner or just pasting each file 1 after another into a hex editor) will get the file structure correct but you will need to manually remake the ToC of the .bin, this is where you might find it hard (i will post info on the ToC below). Although this method is harder it will allow you to have files bigger then the original.
And here is information on the opening.bin (taken from the PAL version of the game but from what i understand it is the same on the NTSC-U version, I'm unsure about the NTSC-J version)
OPENING.BIN is a archive of LZS and uncompressed files, when extracted from unbinlz files 0-7, 17, 18, and 21 are lzs compressed and the rest are uncompressed files
If you open OPENING.BIN in a hex editor the first 92 bytes or 0x5c of the file are the ToC of the BIN, to read the table of contents you read it 4 bytes at a time and in Reverse.
So for example if you look at the start of OPENING.BIN the first 4 bytes say 5C 00 00 00 what this means is the first file in the BIN is actually at 0000005C
To save time i already wrote down where each file started so this should make things faster (it lists which file is which in the ToC and where the file is in the OPENING.BIN)
Code: [Select]
Code:
OPENING_005C0000000000005COPENING_01301D000000001D30OPENING_02683F000000003F68OPENING_032C6500000000652COPENING_04E0870000000087E0OPENING_05E8A600000000A6E8OPENING_06B8C800000000C8B8OPENING_07C4E400000000E4C4OPENING_0890FF00000000FF90OPENING_097400010000010074OPENING_105801010000010158OPENING_113C0201000001023COPENING_122003010000010320OPENING_130404010000010404OPENING_14E8040100000104E8OPENING_15B0050100000105B0OPENING_169406010000010694OPENING_17541B010000011B54OPENING_189CC501000001C59COPENING_1918FC01000001FC18OPENING_2038FC01000001FC38OPENING_2158FC01000001FC58OPENING_22E8460200000246E8
Anyway all this information should be more then enough to fully edit the OPENING.BIN, i hope this helps and please let me know how you get on (also the file joiner i used when testing was called "FFSJ" but it requires you to rename the files first, but i am sure there are lots of binary file joiners out there where you wouldn't need to rename files first)