Step #68 in the Expanded Vanilla list
I recommend using the "Full Cephalopod" version because it gives Telvanni guards a distinct look that fits the existing styles of the game.
Note that Delta Plugin is required for this to function properly! If you're following a list, that will be one of the last steps.
Read the mod description and check out the pictures for details about the differences between each version.
Yet Another Guard Diversity - Full Cephalopod.ESP