I'm unclear about the alternate texture lists and how they are used (meaning: what are they for).

* I have a mod in progress that seems to require a texture swap on an existing model, and wondered if this is an avenue to investigate further.

If anyone knows more about this, I'd love to learn some of it. I have looked at the http://geck.gamesas.com/index.php/Model_Data on this but its pretty basic.
It looks like the game can overide a NIF's reference to a texture file with another one... Is this scriptable in any way? What I would like to do is re-texture a loaded NIF at need, then swap back to the original texture (until the alternate is needed again).

Any insight is much appreciated. :tops:

With texture sets you can override a models default textures, yes. Check the VaultSuit21 outfit for an example, it applies new textures to the vaultsuit. It's extremely useful for making variant outfits since it doesn't require you to copy and edit meshes, like you did in Oblivion (IIRC).

AFAIK it's not possible to change textures in-game. I don't think they implemented it in FOSE, but you could request it for NVSE and hope for the best.

Thanks :tops:,
I will indeed ask about it, if I can't find a faster solution.