Well aren't you in luck. 2 years ago I was struggling to wrap my head around this very thing with FF7. Lemme see what I can recall....http://forums.qhimm.com/index.php?topic=16930http://forums.qhimm.com/index.php?topic=17044.0https://www.youtube.com/watch?v=s_QBELkbaBs
I hope this helps.
The gist of the video tutorial is that we use something called FF7Tools, and we use "unbinlz" to extract the contents of the archive "OPENING.BIN". I was trying to mess around with the title screen.
"unbinlz" extracted the contents, and the title screen was "OPENING_17.data".So the data in that scenario was that different files are at different offsets, and they were all lumped together in one file: not all the files were compressed. But they were all connected together in the ".bin" file like some sort of human centipede. To add to the confusion, "unbinlz" then decompressed the compressed files at the same time.
So I made my changes to "OPENING_17.data" and and had to compress it with "lzss" (it should generate a new file, that is your compressed file).
In Hex Workshop (or whatever hex editor you prefer), we would go to the offset where "OPENING_17.data" was stored, then select the chunk of data that is the same size as my newly compressed file, and flood that block of data with 0s. Then go back to the offset where "OPENING_17.data" was stored, select the chunk of data that is the same size as my newly compressed file (it turned all into 0s if you recall), and paste into the selection (overwriting all those 0s).
But in my case, the files I would make were either smaller or the same size as the original file. If the file is larger...then it's a much more complicated situation that even goes over my head.
Anyway, we saved the modified "OPENING.BIN" which had the compressed "OPENING_17.bin" pasted into it's appropriate space, used CDMage to reinsert it into the game, and I can see my bullshit title screen hack after that.