I feel like I'm just missing something here, because I can't seem to find a function to automatically give the player or an NPC a specific effect (enchantment, poison, whatever), an object effect.

You cant really give the player an Object Effect -> Object Effects are attached to weapons, clothing and explosions.

Object Scripts are attached to base object references and as such can not be dynamically applied to anything.

Magic Effects are Actor Effects, use CIOS to have an effect applied to any actor -> Use AddSpell to have an ability attached to an actor.

Try making a perk and sticking it on there?

It's clear that perks do work on NPCs at least as of this .exe version. They add a perk to followers when they are hired and remove it at unhire.

I need it to happen once. Basically, I have a mod that makes guns and sharp melee cause bleeding damage post-impact. This bleeding can be stopped by bandages. I want healing powder to not stop it entirely, but reduce the level of bleeding (there are four levels, each their own Object Effect, different weapons have different bleeding levels), basically I'd need the script effect for the healing powder to dispel the bleeding, and activate one level lower bleeding.

Oooh! I have it, thought of it while writing this. I'll have the healing powder have an extra healing effect (four actually, one for each level of bleeding), that additionally heals enough to compensate for whatever level of bleeding is currently affecting the player! Thanks anyway guys.

It's a bit of a hack, but CIOS works with object effects, you just have to set the duration of all the base effects making up the object effect to something other than zero, meaning the object effect will eventually wear off. It's the way most needs mods apply penalties, because it causes the effect to show up in the eff. tab of the Pipboy.

CIOS?

CIOS is short for CastImmediateOnSelf