First: fantastic forum you have here.
Second: I want to thank user gjoerulv for posting the savemap data for FF9 in this thread: http://forums.qhimm.com/index.php?topic=10754.0
In particular I was stumped about figuring out where the trance offset was, and was about to resort to trying every byte to see what worked. I actually don't bother with editing mcr files anymore, since I realized that epsxe save states are just gzip files. Editing save states usually avoids the need to reverse engineer checksums. I typically write Python scripts providing a command line interface to edit what I want.
Third, since this is my first post:
Back in the late 90s/early 2000s I did some save-state hacking for zsnes roms. Before Python, I typically used a hex editor to directly modify files, although I did create some win32 gui tools for editing Final Fantasy IV
*.zst files. It was nothing compared to the kinds of serious projects that others in the romhacking community were up to but it's what I wanted to do.
It's really nice to see there's a community devoted to this kind of thing.