T-Engine allows all game modules to support addons and Tales of Maj'Eyal: Age of Ascendancy is taking full advantage of them to allow players to customize their game.
To install an addon you simply have to download the .teaa file and place it in your game's game/addons/ folder, unless the addon explicitly gives special install instructions.
To upload new addons you need to be granted permission. Simply send a message throught the contact form saying what you wish to upload first.
This is only to ensure no spam gets on, once you have permission you can upload as many addons as you wish.