I've got an ancient, maybe 40 or 50 years old, switch for the immersion heater in my airing cupboard. It's a thin-ish one, mounted on the wooden door frame.

Increasingly, it gets hot in use and has started to smell slightly (I think it's a heated plastic type smell).

I want to replace it with a switch like this https://bit.ly/336ClVA , mounted in a steel back box, on the wall next to it. Am I allowed to do that?