You will find multiples of many files in the game, as many files are re-used in the different modules of the game.
While you could edit a NPC's utc file in KOTOR I and plop it into override to make some changes, in TSL you cannot do this as much because OE re-used many of the game files between modules, and as such the game can get messed up when we place these files in override because though they have the same names they do different things, so in TSL we have to generally use scripting or other methods to make enemies tougher.
I might suggest a Mod like Achilles Game Rebalance Mod (
http://www.freewebs.com/achilles01/), I believe you will find the game to be more of a challenge, but not overwhelming. If you love self-abuse you can use Achilles Mod plus Beancounter's Hardcore Mod (
http://www.pcgamemods.com/mod/10900.html), then you can be in for a world of hurt! :xp:
As for learning about KOTOR and TSL modding, you can browse the many Tutorials we have in the locked forums you see above... there is much reading, but that is the information we have.
I hope this helps! :D