Allow me to provide you with an alternative method for duplicating a closed-period estimate in QuickBooks Online (QBO) without entering a password, Luke.

When you close the books in QuickBooks Online, the estimates are included. However, estimates are not impacted by the process of closing books. They will remain in your QuickBooks Online account and can be accessed and modified.  

To create a duplicate of the estimate, navigate to the All Sales section, locate the desired estimate, and click on the dropdown arrow linked to the specific estimate you intend to copy. By following this method, you can prevent the system from interpreting your action as an attempt to duplicate the estimate, which would typically prompt a password request. 

If you want to change the closing date or the password you used to lock your books, you can easily edit them by performing the steps in this article: Edit your closed books. 

I've also added this article to help you with your future tasks with QuickBooks: QuickBooks Online year-end guide and checklist. This contains sub-articles to give more insights into the different types of processes.

Please comment below if you need more help with this process or if there's anything else I can do for you.