You can also switch screenshots to JPG instead of default BMP since vastly larger BMP images are really only useful if you're planning to do photo work and want the best source possible.
SET ScreenshotFormat "JPG"
And for higher quality, you can change with a 1-2GB VRAM GPU:
SET MIP_LOAD_SKIP_LEVELS
to
SET MIP_LOAD_SKIP_LEVELS "-3"
If it causes lag, try lowing it to "-2", or "-1".
You can also add these below SET MIP*:
SET SimultaneousCharacterLoadLimit.2 "10"
SET SimultaneousCharacterDestroyLimit "10"
AMD users _might_ have better performance changing as well:
SET GraphicsDriver.7 "D3D11"
to
SET GraphicsDriver.7 "OPENGL"
Set the file to read-only when you're done, or updates to the client will nuke the changes. Or, create a backup of your modified file, and manually re-add the changes after each update.