I assume you're talking about the ones that start with a 4 on the first line? No, you can't separate them unless you're using an AR Max. Any other cheat device only does that kind of write for 32-bit/4-byte values.
As far as the code value goes, you can do anything from 0 to whatever the max allowed for the field type is. The values on the help page are just common examples. For 100, just pad out 64 with as many zeroes on the left as required to fit where you need it. In the codes for all stats on all characters, that'd be 00640064.
Edit: For what it's worth, there are ways to do what you're asking on other devices. It just requires using the cheat device to insert what amounts to a small program via cheat codes. My copy of Suikoden III is in a box in the basement somewhere along with all my 3 generations ago stuff, though, and it's not something I could generate on the fly, from memory, for this game anymore. You could try requesting it on a retro-hacking site like gamehacking.org
. I'm about 60% sure I actually did make a code like this as an example in a tutorial I wrote ages ago. I'm a bit of a packrat for stuff like that, so I'll post it if I find it. The bottom line is that your quickest path will be to use an AR Max, if you have access to it.
Edit 2: Nope, sorry. I found the tutorial, but it was a code for maxing out all the skills for all characters.
Edit 3: I actually found a pretty good, marked up disassembly for the game while I was looking. If you don't mind being a guinea pig, this should work, I think:
200C500C 24010064 <--0064 at the end here is 100 in the stat. Change it to whatever you like.
If it doesn't work, it's at least 90% of the way there. If it does what you like, I recommend saving (preferably a new save), and reloading the game without the code. I didn't have a convenient chunk of code identified that wouldn't require weird instructions, like go into a shop to have 100 MAG, so it's hooked into where the game reads the controller input. It's deliberately setup to only run once, but not having it on constantly is still a better plan.