Another way to control the HDMI switch would be to have an IR transmitter LED sending the same signals as the TV remote and switching the to channel 1 or 2.

IR blaster won't work on my Raspbian...

I followed several tutorials like this one and that other one but it failed every time.

The I found this post explaining there is a bug on some Raspbian kernels. My Raspberry run a 3.18.7 kernel and it is affected. I tried to boot on an OpenElec with a 3.17.16 kernel, and then my test code was working.

So I'm postponing the IR blaster part since apparently there is also a performance problem when using this method