There isn't a better way that than you suggest.  The system isn't designed for the case where the deposit has the wrong date - so wrong that it is on the wrong side of the dividing line.

Perhaps, have your client review/verify the transaction dates in their account register before creating the accountant copy.

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That noted, the date of the deposit, being wrong, won't really break the reconciliation.  You can complete the reconciliation and then return the file and then tell the client to fix the date after  merging your changes.