Is it impossible to import something new into the game ?

[IAmGonnaBrown]

Specifically, a mesh with textures and animations that does not exist in the game itself. For example:

I've made a triangle-shaped table. And I want it to be inside DS2 as a prop to place around
Or a Royal Swordsman, that have un-broken armour with some decorations on it using animations of a player character
Or some weapon models pulled out from other FromSoftware games.

Is adding such things into the game, possible ? Cause from the mods I've seen so far, making something that isn't a re-texture of already existing mesh, I've got an impression that doing something like that, is impossible to make while it looks like DS3 and DS1 don't have such a limit.