Skybox Blending. 5 Skyboxes instead of 2?

I know right there was similar Questions like that before but no clear Answer was found.

I am using the standard Skybox Blend Shader for the Day/Night transition, but i want as well including Weather and SunRise/SunSet Skyboxes too. As you realize there are more than 2 Skyboxes needed than only 2 ' BlueColors '. GameCreators of great Games like ESO was able to do it, so i would not doubt that this would be possible.

my question is: How can I extrude my Blendshader to work with 5 Skyboxes instead of the 2 standard ones?

( don't tell me by copying the codes of tex2, that didn't work. )