This leaflet is a lie. There is almost complete freedom to interchange between Bank and Monument. The only real change is that the new tunnel from Monument to the Bank DLR level is closed, and that there are some one way systems in places, depending on the time of day. The entrance in King William IV Street seems to open past the normal 9pm weekday close, since this is the only "official" route to the DLR / Northern Line.
Some signs have been covered up so that newbies and tourists cannot find the quick way from A to B. My guess is that the fire and safety rules would not allow the scheme described in the leaflet!