Editor Modes
You can easily create new editor modes
I have a Vertex Snap Editor Mode you can check out the source code for
the 4.1 Source code is part of the Download file
This Editor Mode plugin is currently a pull request on GitHub
you can check out a video here!
https://forums.unrealengine.com/showthread.php?3275-Giving-my-Vertex-Snap-Editor-Feature-to-Epic-as-Pull-Request
Rama