You should customize the deployed assembly, there are a lot of things you cannot do inside the dashboard maintenance “customization”
Yes you can refresh the dashboard from inside the customization all you need to do invoke the refresh command.
MainController.AppControlPanel.HandleToolClick("RefreshTool", new
Infragistics.Win.UltraWinToolbars.ToolClickEventArgs(MainController.MainToolManager.Tools["RefreshTool"], null));