I was trying to add all our old news stories to a Plone site. I was having a problem with it not accept date changes when I tried to make News items in the past. It looks like you should be able to do this in Plone but I had no luck there.
1: Make the news item in Plone.
2: Publish it.
3: Look at the news item in the Zope interface.
4: Modify the Effective date in Zope. Save the changes.
5: Look at the news item in the Plone interface.
6: Make an edit to the description. (E.g. add the word "Changed" to the end) Save the changes.
7: (If necessary) Make an edit to the description undoing the change. (E.g. remove the word "Changed") Save the changes.
Making the edit in Plone forces the change you made in Zope to become live.
Note: The terms Effective Date, Effective From Date, Published Date are all the same thing.
Note: DO NOT re-publish the news item or you will have to do this again. This in effect means you must have permission to edit pages that are live.