Admin Tools for ArcGIS℠ Online allows you to export as many Items, Groups, or Users as you want to an excel friendly format (.csv). You can edit the content in excel, or even add new content quickly & easily. Whenever you go back to the Admin Tools to upload the file you just edited, it will updated any of the content that you changed and/or make new content that you added.
Get the App here on the ArcGIS Marketplace