There's more than one way to do this.
The way to do it in the editor is create an add-on project, more on that here:
http://docs.larian.game/Working_with_projects.Make sure to set it to target project for and load data from Story. (you might not actually need to load data from, but I'm not sure so just do it :P)
After that load it up and open the stats editor. I don't think there's a guide for that yet. But it's on the top bar of the editor.
Then inside the stats editor look for Projects>Shared>Stats>Character
Inside there you'll find an entry for HardcoreNPC. Right click that row and then select "override in YOURMOD NAME". That will create an entry for HardcoreNPC in your mod which will override the normal settings and copy all the defaults to start.
Then move over to the right side and modify the values. By default it has an armor, magic, damage and vitality boost of 50. You can just start lowering the number till you get what you need. Compare it to the "NormalNPC" or "CasualNPC" entries to see the differences.
Save it all up and try it.
