public IReadOnlyList<string> GetFallbackTools()

// A fallback tool is the tool that will be activated when an editing tool
// is deactivated; (when the Escape key press for example)

// To register a tool as a fallback tool, add the following into your
// add-in's config.daml file

// <updateModule refID = "esri_editing_EditingModule">
//   <menus>
//     <updateMenu refID = "esri_editing_DefaultTools">
//       <insertButton refID = "MyAddIn_MyCustomTool"/>
//     </updateMenu>
//   </menus>
// </updateModule>

var options = ApplicationOptions.EditingOptions;

// get the list of fallback tools that are registered
var fallbackTools = options.GetFallbackTools();
// get the current fallback tool
var fallbackTool = options.FallbackTool;

// set the fallback tool
// (MyAddIn_MyCustomTool must be added to the "esri_editing_DefaultTools" list)
options.FallbackTool = "MyAddIn_MyCustomTool";