Could you please explain your scenario in more details as well as attach a couple of screenshots demonstrating the requested functionality? Do you want to open the Media manager from the Link Manager similarly as it is possible to open the Document manager from the Link Manager? Do you want to add a search box to the dialog?
You can see how to customize the RadEditor's built-in dialogs in the following live demo: Customize Built-in Dialogs
All the best,
the Telerik team