I need to add a rendering to all of the pages in my Sitecore tree (i.e., items that have renderings, have a layout set, and live under
/sitecore/Content). Content items that don't have renderings or a layout set don't need the rendering. I want to add this rendering to the
layoutHeader placeholder on my pages and the rendering does not require a data source.
Is this something that's possible with the Sitecore API or Sitecore PowerShell? If so, how would I go about it? I'm working with Sitecore 8.1 Update-3.