Go toto open the settings.xml file in the program you have assigned to open .xml files with.
If that program does not allow you to edit the file, chooseinstead to locate the file in explorer from where you can open it in your preferred editor.
After changing any setting simply save the file and go back to the vl editor. Changes are applied immediately, no need to restart!
You can also provide a local settings file via commandline options when you start up vvvv.exe: