But this is just another way of stating the intuition with which this section opened - that in the face of temporary exchange rate shocks, the authorities should not react but in the face of a permanent or structural change in the exchange rate, they should. The trick is knowing, as the exchange rate moves, whether it is temporary or structural.
In practice, it would seem sensible to assume that at least some of the movement is structural, or at least will last long enough to either damage price expectations, or affect economic activity (too much expansion, in the case of a depreciation). So I am not sure that the Ball rule has advanced us much past the intuition.