It uses the new features added in 24w36a which allows you to add custom models and also custom item texures without using custom_model_data.
Here are the commands to spawn the armour:
// Helmet
/give @s minecraft:iron_helmet[minecraft:item_name="'Copper Helmet'", item_model="custom.armour:copper_helmet", equippable={slot:head, model:'custom.armour:copper'}]
// Chestplate
/give @s minecraft:iron_chestplate[minecraft:item_name="'Copper Chestplate'", item_model="custom.armour:copper_chestplate", equippable={slot:chest, model:'custom.armour:copper'}]
// Leggings
/give @s minecraft:iron_leggings[minecraft:item_name="'Copper Leggings'", item_model="custom.armour:copper_leggings", equippable={slot:legs, model:'custom.armour:copper'}]
// Boots
/give @s minecraft:iron_boots[minecraft:item_name="'Copper Boots'", item_model="custom.armour:copper_boots", equippable={slot:feet, model:'custom.armour:copper'}]- Change
copper.jsonand it's contents to your armour! - Replace the
humanoidandhumanoid_leggingsto your textures! - Change the item textures to yours!
- Use
.replace.batand replacecopperto your armour! - Modify the commands in this file to spawn your custom armour!