How To Override Created/Created By/Modified/Modified By Fields

A lot of people ran into issues when trying to achieve the goal. The trick is really simple, you just need to call SPListItem.UpdateOverwriteVersion() instead of SPListItem.Update() or SPListItem.SystemUpdate().
                             

         item["Author"] = web.SiteUsers["sp2010\\user1"];

         item["Editor"] = web.SiteUsers["sp2010\\user2"];

         item["Created"] = DateTime.Now.AddYears(-50);

         item["Modified"] = DateTime.Now.AddYears(50);

         item.UpdateOverwriteVersion();