Hi Ming,
GNPS looks awesome! We absolutely would like to support you in integration.
Here is a tutorial from a year ago that shows several aspects of NDEx-Cytoscape-R-Python intercommunication.
The javascript section demonstrates downloading a network into Cytoscape, loading and saving a network from/to NDEx, and displaying a network with Cytoscape visual styles.
That would be enough to add "open in Cytoscape" and "save to NDEx" to the GNPS downloader.
But definitely bring us in when you are ready to try things. We intend to upgrade our libraries and make this simpler, and it seems to me that your applications could be great driving cases.
Dexter