Can I create level editor with UE/UDK?

I wanted to, before digging in too deep, know whether by using the development kit/engine framework, would I be able to build a custom level editor?

One that would support much of the crucial features from the original UE editor: light baking, material building and project building. Would the application framework allow me?

If the answer is YES, please point me to the right direction so I can further explore.

Thank you!