You can re-edit the post only if you feel that is utter necessary. If you want to add more information in a particular resource which you have already posted its better to write a new resource. A resource with 20 line with good keywords is equal to a resource of 1 page with no proper keywords.
But as of my knowledge, editing the content after some days may not be much use because Google may have already indexed it.
A S Kranthi Kiran