Is it possible to edit the sub-sub-GameObjects of a prefab in the assets window?

As the question says, is it possible?

For example, I have my player prefab which is structured as such:

`

▼ Player
    Graphics
  ▼ RecoilReceiver
        MainCamera 
        PlayerGunRenderer

`

I basically want to know if it’s possible to edit the “PlayerGunRenderer” without having to add the prefab to my scene.

It is not possible, you have to add it to the scene, edit, then apply.