Optifine sometimes have cosmetics (eg: Christmas hat), and I would like to see them on this mod, is this possible ? Thanks in advance for your answer

I never heard about optifine having any cosmetics besides capes, can you give more context on that?

Basically there is a service called Cloaks+ that uses Optifine playermodels/cosmetics to show custom 3d models to the players. This system is also used by Optifine themselves to put Christmas Hats to players.

Api endpoint are: To get players cosmetics: http://s.optifine.net/users/IGN.cfg
Actual cosmetics files: http://s.optifine.net/items/COSMETIC TYPE FROM CFG FILE/{model.cfg (for model specifications) OR texture.png(assets)}

Cloaks+ is a third party service not affiliated with optifine, and the way it works is kinda weird so I don't think I will support it for now.

I don't ask support for Cloaks+ but for Optifine playersmodels (eg santa hat)