Looks like mipmaps issue on modded texture import is finally figured out:
(Comparison is done at max zoom out and captured externally, that's why it's low-res. You can find full res comparison in attachments).
Yeah, took me long enough to figure it out, but basically imported texture must have mipmaps baked in and also be in DDS format. For generating mipmaps and convering .png to .dds you can use Nvidia Texture Tools Exporter:
And for import I know only one tool which can import back DDS without issues - UnityEX. I don't know if free version can import it back, but paid one does for sure.
Now, all these textures packed back in Bundle files will bloat filesize by ~2.5 mb for each edited texture. This can be avoided by unpacking Bundle files and then using "Write to .resS" in UnityEX texture import options.
So yeah, this is actually a big deal for Tits mod, since it allows me to rebuild outline textures so it will look like the originals and it looks like mipmap issue is resolved.
PS: I still like the way no-outlines version looks like, but since major texture issue is fixed it's just an option now.