I searched the bug list as best I could, but did not see anything relating to this as of yet.
As of my installed plasma-nm version, 4:5.14.3-0ubuntu1~ubuntu18.10~ppa1, I do not see a GUI way to set the "metered" property of a NM managed connection in the "Connections" dialog. I would like to see a dropbox or toggle to set a specific connection's metered property to true / manually set. Of course, I can dig up how to do this on command line periodically, but that means more searching and using bandwidth on very expensive / tight connections to remember how first.
Git commit 4b549b2d37d8f942b6f821077b87baede447f791 by Jan Grulich.
Committed on 14/11/2018 at 13:43.
Pushed by grulich into branch 'master'.
Add metered property to general configuration
M +5 -12 libs/editor/settings/connectionwidget.cpp
M +156 -162 libs/editor/settings/ui/connectionwidget.ui
*** Bug 403898 has been marked as a duplicate of this bug. ***