But the person on the ladder supporting the weight also has to unscrew the hinges from the side, the sash will likely have to be fully open to reach the top corner screws which means the person in the inside will struggle to support anything and once you unscrew either side then the sash suddenly becomes rather heavy, couple that with the screw holes in the new hinges will be in a different position to the old so now your in a whole world of pain, trust me it's easier to deglaze and unscrew the sash and bring it in