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The only way to modify the behavior of the navigation would be with a template for it. You've mentioned modifying the delay of on mouse-over event. In order to do that, you would have to set the ExpandDelay property to your navigation. Here's some more information about that. RadControls page is also the best source for samples and detailed information on the client-side API of all controls, so you can always refer to it when creating a custom navigation. I have prepared a sample custom template for you:
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="RadMenuDelay.ascx.cs" Inherits="SitefinityWebApp.RadMenuDelay" %>
Add this to an ascx control and enter the relative path to this control in the Desing settings of the navigation - Custom template path.
All the best,
the Telerik team
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