If RPG with the ability to change armors and clothes are made, how is it done? I mean the 3d side mostly

If i make normal character, that has flat clothes, it would be easy, just change textures, but question is about armors, which have totally different models.

So are only armor models recreated or character model with armor? How is it imported into game engine, only armor or character model with new armor?

If person changes armor in game, will game swap the hole model or only the armor part?

if only the armor part, then how the movement animations are done, are armor models animated on characters in 3d programs or what... :D