Thank you for your interest in RadRichTextBox.
If you are going to disable the confirmation dialog, I would suggest you handle the UntrackableCommandExecuting event of the RadRichTextBox and change its Handled state.
Please take a look at the following code snippet which illustrates how to accomplish this:
.editor.UntrackableCommandExecuting += editor_UntrackableCommandExecuting;
sender, UntrackableCommandExecutingEventArgs e)
I hope this helps! Let me know how it goes.