/goop nbt cModelData <player> <slot> [±]<value>[%] [objective]
This edits the NBT data of the item(s) in the specified inventory slots.
Also stores the final total value of custom model data as the score of <player> in the [objective] objective.
Player whose inventory items' NBT will be edited.
Supports a few vanilla selectors.
[1.6.5] May be an Entity (dropped item) UUID
The slot in the player's inventory in which items will be re-modeled. To read on slots see Inventory Slots.
Examples: mainhand, offhand, chest, feet, any, 0-8, ec*
The operation to apply to the custom model data of the item. See Plus Minus Percent page for full explanation.
The name of the scoreboard objective that will store (ten times) the final custom model data value.
You can use +0 as the value to read the custom model data of an item
Then, you may make it take two paths with a MythicMobs skill, one that sometimes edits the CustomModelData into a 'powered' state, and another that reverts this change but also executes cooler particle effects.
/goop nbt cModelData cocopad mainhand 4
Changes the custom model data of cocopad's mainhand item to 4
/goop nbt cModelData SugarFlow legs +0 cItem
Sets player SugarFlow's cItem score to the value of custom model data of their equipped leggings. Fails and doesnt do anything if they have no leggings equipped.