To open a List in edit mode and add the new Web Parts you usually need a SharePoint Desinger. But there is a trick, how to open a List in Edit Mode and have the “Add Web parts” window is displayed. Everything you need to do is to add "ToolPaneView=2" parameter to the List URL.
For example, if you have the Forms list with the following URL http://t1:85/Pages/Forms/AllItems.aspx, applying the new parameter to the URL as http://t1:85/Pages/Forms/AllItems.aspx?ToolPaneView=2 you get the following screen
There is no SharePoint Designer used and no customisations to the page that require unghosting from the site definition.