i know next to nothing about hacking ps1 games, but i have hacked sonic adventure PC.
it might be worth a try to try to open the .bin (or it might be another file, im not sure) ior whatever file contains the models for the game in a 3d modeling program and then search through them, theirs a good chance youll find unused models of objects and maybe characters.
as far as iso's go, its basicly the same thing as copying and pasting the data, but a complete copy, so you can reburn it later. if you download the chrono cross iso (legal if you own the game) and want to open it, just get winrar (like winzip but better) and open it up like a zip/rar file. it acts exactly the same.