It's dangerous because it could attract the current and spark. This could cause a fire.
A magnet can't attract a current towards itself. Remember Fleming's laws.
It is true that magnetic fields deflect currents rather than attract them, in the sense that the force on the charges is at a right angle to both the field, and the velocity of the charge (relative to the field). However, under certain circumstances, a magnet can attract current towards itself. As I understand it, this is part of the part of the explanation of the auroras. Charged particles from the solar wind get "trapped" in helical orbits around the Earth's magnetic field lines, and wind up following the following the field lines to either the north, or south, magnetic pole. Of course this situation with the Earth's field and the auroras is completely different than the one with the yet-to-be-constructed magnetic switch plate. But just to be pedantic, there are situations when a magnet can attract current, or at least charged particles, towards itself.
<pedant> You're referring to the "cyclotron" effect I think ? but there, the field is still perpendicular to the motion, and no magnets have been hurt in the process.... </pedant> Steve
It probably won't be "up to code" since the cover will be too easy to take off, but other than that it sounds mostly harmless. Regarding interactions between the current in your wires and the magnetic field of the magnets, I think the worst that could happen is maybe some vibration or buzzing noises, but probably only if the magnet is right next to a current carrying wire. I say, "Do it!", and see what happens.
BTW, if you live in a country where they don't have electrical code, then obviously that junk about "up to code" need not apply. ;-)
That depends on how much heat goes through the area, heat can ruin magnets.
????? I don't think the Curie point for a practical magnet, for holding a switch plate on is likely to be an issue here.
Holding it on probably isn't a problem, it's taking it off. I assume you want this easily-removed for some reason? L