I just did a quick test where I altered movement speeds in AIbutes.txt and it did nothing at all even though I rez'ed it and ran it as a mod.
The player will probably not use any of those templates, but AI will. That's how I configured the new characters in the ROH mod.
I can't say this for sure but from my best guess I'd say that most stuff that can give the player a advantage over other players (even singleplayer) would be stored in one of the dll files. Which would mean that it would be in the source code itself.