Changing custom import settings at RUNTIME

I'm currently working on a project where Textures need to be easily swapped in and out of a single build of the game. To that end, I'm taking an intermediary step where the Textures are still in the project bundle. However, the texture import settings need to be specially set for the game in question, but I want to leave all the other textures alone.

This needs to be done at runtime, and thus cannot use any editor scripts.

EDIT: It seems I was confused about what RenderTextures were. Basically what I need is to take a datapath to an image file not in the project bundle and read that into a new texture in using WWW with custom import settings.

Specifically I need to tweak anisio settings and read/write access.