The exterior triangles do come off.....its a bit of a fiddly job but they definately come off.
I know this as i treated mine to a carbon skinning!
If i remember rightly, from inside the car, gently prize off the interior triangles and you will see a "torx" bolt...(i think, been a while since i did mine)
Obviously undo this bolt and "jiggle" the exterior triangle passed the rubber frame (wind the window down to make life easier)
In haynes manual style, replacing is a reversal of removal.