... is a toggle switch (I was looking for that Word) so the LED is supplied once the button is on ON position I will try like that, I dont think I would kill the Arduino ?
I don't know if can damage the Arduino...or disturb the matrix...
Just for one LED the ideal and safety solution is a DPST ON-OFF toggle switch, since have two lines of pins (is two independent switches controlled by one lever), you can wire LED with his own power source, can take for RAW pin.