Ubuntu Gnome 17.04 - panel icon refresh command?

I have two "homemade" indicators which change their icon on the top panel using pkill command and then restarting a python script, but unlike Unity top panel and also unlike "professional" indicators, the new icon for my indicator is not displayed unless I restart Gnome Shell (e.g. Alt+F2, r).

I guess there must be a command to tell Gnome Shell maybe to merely refresh the top panel icons or even merely the icon for that particular indicator???