Is there a way to modify News posts and comments without deleting the post and c

Editing via the UI is not available as a feature in the product. Only deletions.

Thanks Eduardo.
My concern is where comments need to be moderated, or were accidentally posted and the author wants them retracted.
Would be a nice future feature.

We've had a similar request for retraction and editing, but had a requirement for an audit history of all changes. We eventually took the view that the users shouldn't post what they didn't want read by the relevant groups, and a small about of user training took care of that.

As of Appian 7.9 a user can delete their own post if no one has commented yet. This is good for the "accidental post". There is no edit however. If a post has a comment then an Administer would have to be contacted.