I've put my property up for sale and it seems that Paris City Hall intends to use its right of pre-emption. Can I withdraw my declaration of intent to sell?

Yes, provided that the local council has not yet exercised its right of pre-emption (art. L.213-7 of the French town planning code). Indeed, the seller of a property subject to this right of pre-emption and having filed a DIA may unilaterally retract his offer to sell until it has been accepted by the beneficiary of the right. So, if you have not yet received a formal reply from the Paris City Hall indicating that it is pre-empting your property, you can still withdraw your offer to sell it.