I scaned your online docs and yEd help files for a way to define custom node types.
I am trying to model a directory structure using yEd. While I can use the text fields of UML nodes to list the objectClass, attributes and their values of each entry, this becomes pretty cumbersome with multiple instances and multiple attributes per instance. Also, I cannot differntiate between mandatory, optional, multi-valued, ... attribute types.
So, I would like to create custom node types for object classes and "instantiate" them in a graph structure. Somehow, this smells like a feature request... ;-)