ADD this character to player

You don't have to do anything. Everything is added automatically when the patch is initiated.

ADD this character to your partner

If you want to add spell to NPC:

1. Open console
2. Select NPC (click on him -- the name will be appeared in a console title).
3. Type:

AddSpell "js_gameplay_character"

You can check result after previous action:

GetSpell "js_gameplay_character"
BONUS: The NPS will be able to use any weapon, not just the one in his skill table, and will do so automatically, since the ability increases the attack to 1000. And hit the target will also almost always, no longer annoying you.

REMOVE this character

From player:

Player->RemoveSpell "js_gameplay_character"
From NPC:

Open console, select NPC (click on him -- the name will be appeared in a console title) and type:

RemoveSpell "js_gameplay_character"