If you are still looking for this, the second link is how to change attack type with triggers though it is a bit limiting even so.
https://www.hiveworkshop.com/threads/trigger-to-change-damage-type.292516/
https://www.hiveworkshop.com/threads/change-unit-attack-type-damage-and-range-in-game.299634/
https://www.hiveworkshop.com/threads/trigger-to-change-damage-type.292516/
https://www.hiveworkshop.com/threads/change-unit-attack-type-damage-and-range-in-game.299634/