I'm new user of jBPM, I want to know how to modify the user interface of GPD to modify and add new buttons for the creation of a workflow diagram.
The buttons that I want to add are a set of graphical elements for BPD respecting the BPMN and using personnalized attribute.
I am not sure what you are trying to achieve, but you should be warned that the GPD implementation will undergo a major refactoring in the coming months and that extension points will probably be broken.
Adding buttons to the palette and associating behaviour with it is possible through the provided extension points in the plug-in. Look at the plugin.xml file.