Quick questions about what addon can and can't do
 

Can an addon replace textures used on 3D meshes / object? Or only 2D UI stuff?

Can an addon turn an object into a light source? Not necessarily making it interactable, but make it glow like a Varla stone?

Thanks!

Only 2d UI stuff and icons like the ones above group members or added 2d icons (shown as 3d) like HarvestMap adds above e.g. harvesting nodes/chests etc.

Nope, no 3d stuff or effects of weapons/armor etc.
All one can do with "lighting" seems to be something like "Light of Meridia" does.

You can not mod ESO like Skyrim or Fallout 4 and there is no ESOEdit to modify the plugin and no nifskope to change the texture. Those don't exist and are not possible without a CK, which there isn't of course.

Thanks folks. That's what I figured. Would really have loved to reskin some stuff like in Skyrim.