It is safe. You run greater risk of becket breakage and tuning stability problems if you lower the tension on the entire scale. You are essentially lowering the compression on the plate braces. The pitch in the middle seciton will go up a bit but will come down when the tension is restored. This will have no effect on the treble of the piano. I have replaced several set of bass strings without changing the steel wire tension. Newton > Is it safe to remove the bass strings without lowering the tension on the rest of the scale?
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