The bank may technically approve a change to the payment due date, but this isn't an automatic right for the customer, as the date is part of the agreed-upon repayment schedule.
Key points
Request the change formally before the payment is due and find out if it will result in a transitional payment, a schedule adjustment, or any fees.
A verbal agreement from an employee does not constitute a contract amendment.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.