Object modifier

Object modifiers (or OMODs) are modifications applied to a base item. These include regular weapon and armor mods, such as sturdy or heavy armor piece variants, Legendary armor and weapon effects, and so forth.

Resources
From the Modding Resource Catalogue
 * OMODs: What They Are and How They Work by Lively

Gameplay
Some of these modifiers are attached in-game, such as when a Legendary item is found, or when an armor mod is attached at a armor workbench. However, many of these modifiers can only be added or removed via the console.

A single item can have a variety of slots available. These slots are known as "attachment points". For instance, armor items commonly support a Legendary effect, a material mod, a misc mod and a size variant. However, only one mod can be attached to a given slot, so attaching a new mod to an already occupied slot will replace the current one.

Complete lists
Based on the OMOD form types:
 * Armor – can be applied to armor pieces
 * Misc (no form type) – applicable to misc objects
 * NPC – can be applied to certain NPCs
 * Weapons – can be applied to weapons

Attaching/removing mods from a targeted item
The command (or  for short) can be used to attach a modifier to an item. To completely remove a modifier, execute the command (or ).

The most common way of using those commands is:
 * 1) Find the item in your inventory and drop it on the ground.
 * 2) While looking at the item on the ground bring up your console (  key on PC).
 * 3) In the console, "target" the item by clicking on it, and input one of the above commands. (Example: )
 * 4) Pick up the now modified item after exiting the console.

Sometimes the item is too difficult to target in the console because a nearby item is getting in the way. If so, utilize the following workaround:
 * 1) After dropping the item on the ground, pick it up by holding the action key (  on PC). This is the same thing you would do to drag the item around in-game and place it somewhere else.
 * 2) Open the console and input . This returns the refID of the item you're holding in the air.
 * 3) Take note of the returned refID.
 * 4) Enter the following in the console, substituting the appropriate refID and modID:  and hit enter. (Example: )
 * 5) The mod is now attached. Exit the console and retrieve the item from the ground.

Attaching mods to items in inventory
The native Papyrus function allows you to attach a mod to a single item within the inventory of an object (such as the player, an NPC, or a container). This function can be called via the console command (or ).

Example
will attach the mod "" (heavy armor) to the base item "" (metal chest piece) in the target's inventory. You could use this after to guarantee that at least one metal chest piece in the target's inventory will be of the heavy variant.