QuickBooks does not require you to close your books as part of the the year end procedures. However, closing date will allow you to limit the access to the closed accounting period by setting up the closing date password.
Once you set up the closing date password, QuickBooks will require the password every time you try to save any changes that will alter the balance for the accounting period that you closed. This includes adding, editing ore deleting transaction that is within the closed period.
You can set up or change the password anytime. Moreover, if you lost or forgot the password, you can remove the password as long as you are logged in as the ADMIN of the company file.