As far as I'm aware, they could do that (would require proof that it's not a clause from the existing contract though), but... why would Maligan agree to be paid less when he immediately becomes more important?
Far more likely to be the other way around "Whilst were at a lower level, with smaller crowds, smaller advertising revenue and no TV money, we can o ly afford to pay you £XXX; but if we gain promotion, you'll be kept on for £YYY with Y>X.
Which would almost certainly be a clause in the existing contract, and therefore smoothed for purposes of the cap.