Permanently attaching armor to the player

Hello! I noticed that in some mods there is a feature that involves permanently adding armor parts to the player model. In this case, the armor slots remain empty. I noticed this in the Wings mod (1.16.5), the Origins mod (the Elitrian race and the Ikarai race that appeared in the fan add-on), as well as the Vampirism mod and the Werewolves addon for it (vampire eyes, ears and werewolf claws). I really want to implement something similar in my mod, does anyone know how to do this? I have already tried the Curious API, Kleiders Custom Renderer, and also tried to create it using Geckolib, but none of this helped, because the above mods clearly use armor, either created in the mod itself, or from other mods or vanilla (For example elytra from the Elytrians and Icarai wings from the Icarus mod).