I would say no, because you already know that it would not be accepted and you're trying to gimmick your way around the situation. It's a different situation than if you mailed a check on the 26th expecting it to be accepted and then there was an unexpected delay in the mail. Plus if the check is post-dated to 2018 that automatically defeats the attempt. And if the county really doesn't accept advance payments, they may return your check, or credit it to 2017 taxes and then issue you a refund will be a taxable recovery next year.
