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In this case they're different URLs. But I believe generally the easiest way is to append some nonsense parameters to the url.

> the easiest way is to append some nonsense parameters to the url

I would advise against that...

Usually there's a "timeout", which will let you resubmit if it has been a long time since the last submission.

But in this case, the URLs are actually different, though they redirect to the same canonical version.

Your resubmission actually counts as a single upvote on the previous submission. I think this is in place to prevent too many duplicate stories.