The command is like kwriteconfig5 --file plasma-org.kde.plasma.desktop-appletsrc --group Containments --group 20 --group Wallpaper --group org.kde.image --group General --key Image --type string "file:///foo.jpg" But that won't change wallpaper immediately unless restart plasmashell.
Correct. Kwiteconfig is generally bad for plasma as you need to know ids. See the plasma scripting api.