Modifying generated texture and asset stripping

We're redoing our UI and are using the new Sprite Atlas assets. Generally speaking they are quite good to work with, we can still get sprites from strings in code which is nice. The fact that 2018.2 will add support for CRUD methods is great to hear too, that is definitely something that is missing right now.

I have two questions though:

- Is it possible to modify the generated textures, like we can do with regular Textures on import? We'd like to customize the mipmaps, but there doesnt seem to be a way to get access to this texture.
- Are sprites that are unused stripped from a build somehow? I do feel like this would be a good addition, or at least as an option on a per atlas basis.

Thanks so much!