At least on 747s opening the 'armed' doors from outside will not blow the slide.
On a B737, opening the 'armed' door from either inside or outside will blow the slide.
Also, the overwing exits are automatically locked when the airplane is off the ground, the pilot gets an indication if this is not the case.
Also, if you are 'lucky' enough to be the one to open one of the overwing exits on the ground, as the FA brief tells you, "open the cover and simply pull the red handle, and the door will open automatically", what they don't tell you is, when you pull that red handle, the door opens very quickly, so make sure you let go of the red handle or you will go out the exit with the door, i.e. very quickly!
