Standing Order 12d of the current model covers the procedure by which the Chairman may indicate that he believes the minutes not to be a correct record of the business of the meeting, however in the situation you have outlined, the issue relates to the decision itself, not the recording of the decision. The minutes should be signed as a correct record of the proceedings, but you should then, at the earliest opportunity, pass a motion to correct the previous decision. Standing Order 7a covers amendments to previous resolutions.