Scene composer plugin

Is there a way to create a plugin for Scene Composer ?
Do we have access to mouse click on view and the ability to alter some node position ?
Can we add new custom fields to Node Properties ?
I’m looking for a tutorial if there is any.

No Plugin but you can check out the sourcecode sdk/jme3-scenecomposer/src/com/jme3/gde/scenecomposer at master · jMonkeyEngine/sdk · GitHub and build your own version.
Note that a lot of code might also be in jme3-core module. Node Properties are done using jmeNode class and relevant subclasses with the makeProperty Method

Edit: Do not Press F1 and use those docs, use the wiki for info.