You put the passability back the way it should be, and then you find a way to make the other two tiles passable. You don't break something that IS working, to fix something that isn't, because then you've forced yourself to make TWO fixes instead of one
So change it back to the original, then find a tile in the B-E set that's blank and has O for passability, and put that over just those two tiles that you want to be able to walk off the edges.
You won't SEE anything, but the passability of the "invisible" tile will override the passability on the tile below. Just make sure, then, that you keep that tile "reserved" so you don't accidentally put an image on it, thinking it's not being used for anything.