I don't think it's possible to change the placement and numbers of enemies on specific spots on the maps.
The app is now accessible at
https://spiritualsuccessor.net/
I'll post some basic "how to" info later, but for now the stuff you can do is pretty self explanatory. You can import gamedatabudnle files, or just go with the defaults which I have loaded for Deadfire's release version. Then you can open some objects and tinker with their values through the interfaces. Finally, you can export gamedatabundle files from the "Export Data" screen.
I'm continuing work on making more objects editable. The next ones should be Movers, Globals, and Recovery times. I also have big plans for improving the interface, error reporting, validation of user input, etc., and these will come around little by little.
Speaking of error reporting, it's possible to click on an object on the left hand side which is visible in the list, but doesn't have a view with a form for it. In those cases the editor will silently throw a console error. It should still be usable if you go and click a "right" kind of object.
Also, remember that it doesn't remember the state of your browser tab, so don't refresh your browser tab if you have unexported changes.