The other concern is how to make a nice transition between two image. Currently, I test it out in unity that I can make a sudden change on Unity Skybox renderer with mouse pressed. But the light effect such as bounce light, the "new sky" color won't affect the object color in the scene. I need to figure it out how to improve it.

And for the transition, I think fading in and out would be much better. I made some research on how to archive it, and I think I need to go for a try on the Unity Shader.