I am trying to install a Shelly 1M Gen4 switch in a three way light switch in Portugal. I read where the Shelly needs a neutral (blue wire). I have a blue wire in what I think is the secondary box. All of the other wires between the two boxes are black. Can I just disconnect the travelers in both boxes from the switches and use one of them as a live line to the other box? I could then just have the one switch/box active. If anyone has a diagram on how three way switches are wired in Portugal that would be a great help.
Why not place a switch in the light fixture, a lot easier. Been there, tried it, done that with a 2 way system.
So you say to install the Shelly in the light box? Would both the switches still work?
Guessing could get you into a lot of grief, from a safety aspect as well as the possibility of wider device damage if you get it wrong.
Ask a qualified person such as a local electrician rather than strangers of unknown skills in an international forum may be a wise, and ultimately cheaper option. Shelly tech support intimately know their devices and may offer guidance. Avoid AI slop for guidance - your life may depend on it!
Yes. This way the three-way switch is controllling the shelly which on his turn is controllling the light. Much easier wiring with less chance on wiring mistakes.
Btw, to make sure. When you're talking about a three way switch you mean you have three switches that ar controllling one light fixture. Switch ing on the light with one switch and are able to switch off with eather one of the other switches?
By three way switch, I mean two switches that control the same light. That's how it's referred to in the US. Four way switch set up means three switches controlling the same light.
So I would need to ensure one of the switches is turned on before the Shelly can control the light?
This is exactly what i ment. Light & shelly in the samen place. Just add 1 extra wire. This is the best option.
Thank you. That really helps. If I can only figure out how to get another wire through these stone walls. 
Fellow stone wall dweller here. Assuming there's enough play in the wires & not more than 3 90 degree bends, you can use an existing wire to pull 2 replacement wires.
But seriously, call an electrician or at least someone who has some basic experience in local wiring standards.
Another easier option is sonoff basic r4/v5. Just install it on the light fixture if there’s space for it
