making a sealed double glazed unit into just 2 peices of glass stood in a rebate that have been drilled into could still be called a double pane unit, but it will never be sealed, if you introduce valves and air flow into a dgu it will never be a sealed unit for the rest of its time in that rebate.i think if you were to place a thermometer on the inner pane of a normally functioning dgu, and a crystal clear one you will find a large variation between the two, the second one would read cooler than the first, thus having less insulation properties.why not give it a whirl and see if the "U" value has changed