I was interested in buying this headlight switch how hard would it be to install
https://imgshare.io/image/X8lw9
https://imgshare.io/image/X8OGF

This was not an option on our cars and there is nothing to move the headlight up and down (no motor). This is an option on my wife's '16 QX60 though.

I doubt you can install this in an M or Q70. Our headlights are not designed with it in mind.

To add to what Ilya said above:

The 03-04 Infiniti M45 had that switch. Generally, if the factory installed something that can be actuated by a switch, they would have already installed the switch/dial/knob that goes with it.

The switch won't do you much good as a headlight switch since the car already automatically does what the switch would have done (see the videos below). If you want to use it for some other function, or to intercept the circuit so that you can trick the headlights to go up and down, then that's a different story.

Video 1 - https://youtu.be/VynBaOFhph8
Video 2 - https://youtu.be/4uBOGwGit7k

I didn't realize the M lights when up or down, I thought it was just left to right (for AFS).

If you point the car at a flat wall at night and ten switch on the lights, or stand in front and watch the lights when they activate, you will see and up-down and left-right movement in the 06-10 models as the AFS adjusts them. However, they were not designed to allow any manual adjustments. Someone found a way to adjust the height, but it's a permanent adjustment and every time you want to change it, you have to go back under the hood and inside the mechanism. They cannot be modified to allow a switch like that.

Another thing that Infiniti removed in the Y51 then...mine definitely do not go up and down or mine are broke (they haven't done it since day 1). Just like the tilting head rests (miss them so much).