As suggested and on behalf of the Arlington Public Library in Arlington, VA - It would be very helpful to have a count of the number of items about to be adjusted and/or a way to export the results in order to understand how these adjustments would impact the system and public services staff.
Bug 25995 may also be of interest - it suggests adding changes to due dates to the circ log
Bug 27248 may also help in this situation. It would allow you to first write a report to find the items that you want to batch extend due dates for and them send that list to the tool.