Edited original question: Horizontal heating supply stack (4X15) runs between 2x8 joists under bathroom. The take off for the above bathroom register is located 4" from a rectangle to round connection (round to downstream register). When installed, the 'rectangle to round' connection point sits below the plane of the ceiling - one corner is 3/8" lower than the joist. The original drywall was installed 'around' this. The ceiling was coming down. I removed a section of ceiling to see why. It showed no signs of having been wet. Just force over time - and the quarry blasting every day - pushed the drywall away.
I asked if it would be safe to jack the duct work up - deform it without affecting anything else. Would the force of the jack cause the take off connection for the bathroom register to fail? The corner of the 'rectangle to round' connection would need to be moved up 1/2". If the take off to the bathroom register failed, I'd have to remove a recently tiled floor.