So how do you pass them? By modifying the GStrv in the projects structure?
@elextr The plugin doesn't pass them at all - it's all done by Geany. Users enter the patterns into Project->File Patterns and if Project is selected in the FIF dialog, Geany uses them. It happens the same way even if the ProjectOrganizer plugin isn't installed, nothing done on the plugin side related to this.
@codebrainz Adding stuff directly to the dialog isn't a good idea - it would stay there because Geany remembers what you enter there and on every project open you'd add more and more stuff (yes, you could parse the contents of "Extra options" and remove what you added but there's a danger you'd remove something what the user entered manually).
So yes, one option is to add some API to Geany to support this but maybe even better is to add an entry with excluded patterns directly to Geany's Project dialog plus the "enable" checkbox as you suggest. And I guess many people would like to see it in the FIF dialog too.