I messed around with scripting for a bit.. I remember when I tried to do some stuff 2 years ago there was some really screwy things going on with certain things.
For starters, the ncs's from the compiler that comes with the kotor tool don't seem to work properly for me, even if its flagged for KOTOR1. I had to use hazard's compiler.
Even with that, nothing I modified would take effect via the k_def_buff file. From my end, it looks like this file is basically doing nothing.. at least for "regular" mobs, that I saw.
Modifying the k_ai_master file definately does work for me. You can SetMaxHitPoints and whatnot, and you see it work in game just fine. I can add 100 health to mobs and I know the mobs have 100 more health. You just need to make sure you set special trigger flags so it doesn't keep adding the health or stats multiple times.