A Google Groups thread asks if they publish an article and it is found on Google News, but then want to make a change to that article - will it be updated?
The answer is no. Google News crawls the page once and will not come back to look for changes. A Google News representative confirmed this:
Currently the crawler crawls a particular article at a particular URL once. So in short, no.
You can get articles completely removed by submitting a written request, but that won't update the news story. In these cases, it is probably best to write a small "postscript" and link to a new story if warranted.
Want an example of a mess up that I personally did once or twice?
Back in August 2006, while at Search Engine Watch, I wrote a dumb typo where instead of writing "Google Has Too Much Money", I wrote, "Google Has Too Much Monday." It got indexed by Google News and showed up like this:

So these things do happen and they are hard to fix.
I do have a feeling Google News is working on something to update articles, but I have no insider information on this.
Forum discussion at Google Groups.

Comments:
Andy
01/16/2008 03:25 pm
This seems to be the opposite of what Google News announced recently: "One example we recently released is a new algorithm to help determine the most recent update to a story. In other words, it lets us find something new that's been added to a breaking story." http://googlenewsblog.blogspot.com/2007/12/quantity-and-quality.html
Barry Schwartz
01/16/2008 03:32 pm
Actually, not really. There, they are looking at new urls, not updated URLs. New URLs with updates to old stories.
Loren Baker
01/16/2008 08:30 pm
Yahoo News however does update articles when their content changes.
Barry Schwartz
01/16/2008 09:29 pm
Didn't know that for sure Loren. Thanks for adding.
James
01/17/2008 07:05 pm
Our site gets checked by the Google News bots every few minutes. After we also added News Sitemaps (may as well,) that are only called by G News every few hours, we found headlines do change when altered after the initial bot pickup but before the next news sitemap call.