Basically, gnome is bad at replacing just the icon for you as a user. To be true, it can't do it properly. So the best option may really be making a new icon theme, or as you did replacing the icons in /usr/share/icons (note: usr, not user)
After that you'll have to run
otherwhise GTK cache and Gnome won't recognize there is a new icon in /usr/share/icons for the icon, because they take the cached version.