It looks like you are editing the DescendantsGenerations.gplug extension. I just tried and removing the "!" works for me.
You mentioned "With the script on the desktop..." If by that you mean you are editing a copy of DecendantsGenerations.gplug on your desk top, that will not work. All standard report extensions are stored in the folder located at
~/Library/Application Support/GEDitCOM II/System/Scripts/Reports
If you create your own report extensions, they are better stored in the "User Domain" or at
~/Library/Application Support/GEDitCOM II/Scripts/Reports
To make the change you want, you can follow these steps:
1. Open the DescendantsGenerations.gplug extension in one of the above two locations using GEDitCOM Editor
2. Uncomment that line you described above
3. Save (which means saving it one of the above locations too)
4. Choose the extension from the Extensions menu to run it. If you used the first location, choose the one in the "System Extensions" section. If you changed the one in the second location, choose the one in the "User Extensions" section.
Note that by default Apple hides the Library folder which can complicate opening those files in GEDitCOM Editor. There are two fixes:
1. To open the extension you want to change, hold down the option key while selecting it from the Extensions menu in GEDitCOM Editor. The correct copy will open in GEDitCOM Editor. You can make edits, save it, and then run from GEDitCOM II
2. If you go to your home folder in Finder and choose menu command "Show View Options" in the "View" menu you can check box to "Show Library Folder" (note this check box only appears when your home direction is in the front Finder window).
I hope that solves it
Regards,
John