This is driving me mad. I went to try this and also read an earlier thread on the subject.
On both threads here about NPCs there's reference to "Pressing N in the Embrace Editor after selecting an NPC you want to modify" and a "Things & Templates window" which opens into an "Override Tab."
Where is this? I assumed this means Embrace from the NOD STK Editor but although I have figured out a few really basic things in there, I can't find anything which has to do with NPCs. Just in case I had the wrong Embrace, I also opened up the game and went to the ST mode (which I think is also called Embrace?) for a LAN multiplayer game. I opened an empty map where you can place objects, people, and so forth by point and click. I tried selecting an NPC on one of those maps and hitting "N" as well, but nothing happened.
This is driving me crazy - what am I missing?
Edit: Ah ha. I was missing a tutorial. LOL I found one which will start me from scratch and had an image of the Things and Templates function. At least I know where to look now.

This is actually fun now that I know which way to go.