Can you re-issue or withdraw a Pay Less Notice?

Yes inside the window, no after it. A Pay Less Notice lets a payer pay less than the sum otherwise due. Up to the prescribed period before the Final Date For Payment, the last day the money can lawfully arrive, a further valid notice can replace the first, restating the sum as at its new day of service; say plainly that it supersedes the earlier one, because two conflicting live notices tend to be read against the payer. After the deadline, the notice served in time stands exactly as served, and no revision, replacement or withdrawal changes it. A payer with second thoughts about a deduction can always pay more than the notice states, because the notice sets the floor on what the payee must receive, not a ceiling on what the payer may pay.

A contractor serves a Pay Less Notice on the 10th cutting a subcontractor to £40,000, then on the 12th agrees one £5,000 deduction was wrong. If the deadline is the 15th, it is still inside the window, so it serves a fresh notice for £45,000 superseding the one from the 10th, and that figure governs. Realise only after the 15th and the £40,000 notice stands as served and cannot be rewritten. That is no trap: the contractor can simply pay £45,000 anyway, because a Pay Less Notice only fixes the least the payee must receive, never a cap on what the payer may hand over.