I need to customize the query widget in CRXDE (the one from Tools -> Query). Specifically I need to be able to add a new button to save queries into some sort of favorites as well as to load them. And a second button in search result widget to export the results into a excel file. Any idea what nodes/templates are related to each widget?
I believe this interface is not designed with overlays in mind. I'd be very cautious about extending it.
While you're still using AEM 6.1, there's a lot that has been done recently about improving the visibility of what should and what shouldn't be customized in AEM.
Furthermore, CRXDE is the kind of interface I really wouldn't like to break because of a bug in an overlay. It's just the kind of a low-level, last-resort UI that I like to be rock-solid.
CRXDE has remained relatively unchanged at least since AEM 5.6 but customising this particular interface could still cause you trouble at a later date when you need to upgrade. And if you're still using 6.1, it's likely that you'll be due for an upgrade to a newer version. 6.1 has reached end of core support and extended support is only planned until 2020
If I were you, I'd consider implementing a custom interface of your own. It might just be easier and you would be free to add further functionality without risking it breaking during an AEM upgrade.