In Scene Builder 1.1 there is the following option File --> Customize Library --> Add Selected. These seems to allow you to select an object like a grid pane and add it an all it's children as a custom control in the library. The problem I am having is that it seems to be adding it with the description of base control (ie. GridPane) and not allowing me to use a more descriptive label for the new control. How do I change the label of the control that I add via this method?
This "add to library" feature is somewhat experimental for now, and we are not yet sure what exact shape it will take in the final Scene Builder 1.1 release.
For the time being, it is not yet possible to choose or change the name of a custom Library element, but we are definitely taking good note of this requirement.