You have to close your short trades two business days before the end of the year.
Stocks settle in two business days (formerly three days).
Options settle in one business day.
I don't think IRS will give you a pass if you attach a note that you did not understand the rules.
If you want to cheat you can change the date, but IRS may notice that your reported gain/loss does not agree with the 1099-B sent to IRS by your broker. That's the chance you take.
