I'm sorry, but this is rubbish. You are talking about editing a file in /usr, which means your fix is guaranteed to break at the next upgrade. And this is not "easy". Or at least not "easy" in the sense that Gnome "is not meant for users who don't want to select their terminal emulators". This is neither discoverable nor maintainable.
What's wrong with sane defaults and a configuration panel?
Edit /usr/share/gnome-shell/js/ui/main.js
Comment this line:
global.display.connect('overlay-key', Lang.bind(overview, overview.toggle));
Restart gnome-shell with this command:
gnome-shell --replace
It's just Javascript, so it's very easy.