In Adventurers League, can you change Full Plate armour into Half Plate?

Question

Playing in AL my barbarian has acquired a set of adamantine full plate armour. As this prevents him from his rage benefits, I was wondering if I could simply use it as adamantine half plate, using the half plate stats?

From the Player's Handbook:

Plate armour: Plate consists of shaped, interlocking metal plates to cover the entire body. A suit of plate includes gauntlets, heavy leather boots, a visored helmet, and thick layers of padding underneath the armor. Buckles and straps distribute the weight over the body.

Half plate: Half plate consists of shaped metal plates that cover most of the wearer's body. It does not include leg Protection beyond simple greaves that are attached with leather straps.

Could you simply decide not to wear the whole set?

Answer 1

Unfortunately there's no official rule that says you can do this.

In a home game, it would be fine. You'd talk to your DM and explain that you can't wear this armor as a barbarian, but that you'd like to just wear some of it and count is as half plate. Most reasonable DMs would issue a house rule saying you could wear some of the armor, just as you're suggesting.

However in Adventurers League you can't really do that. One version of the AL DM rules says:

You’re Empowered. Make decisions about how the group interacts with the adventure; adjust or improvise but maintain the adventure’s spirit. This doesn’t allow you to implement new rules, however.

So the DM is not allowed to let you do this.

I recommend trading the armor away to a character that wears heavy armor.

Answer 2

Half of a suit of full plate is not a suit of half plate

Full plate armour is the type of armour that stands around in haunted houses - head to toe interlocking and interconnected plates of steel all over the body. The classic chivalric knight.

Half plate is armour predominately for the torso and head and is made that way from the ground up. You don’t get it by taking a suit of full plate and throwing bits away. It developed in response to the rise in firearms and lingered through the Napoleonic period in the armour worn by cuirassiers. It saw a brief revival in the First World War and has come back with new materials as modern body armour.

However, you are allowed to sell equipment in AL for half list price. Half the value of full plate happens to be exactly what you need to buy half plate.

This works fine for normal armour but is no good for magic armour which adamantine is. You are allowed to swap magic items of equivalent rarity (uncommon in this case) with other players if you can find one.