Tekl

Ah, I see. Not something the Automation Task could handle, the code is basically Application("System Events").currentDesktop.picture = /PATH/TO/NEW/IMAGE. In other words, macOS is (understandably) seeing the same path and not refreshing the image. There’s no command to force the background to reload (technically restarting the Dock should do it, but that’s quite disruptive).
 
Changing it to something else and back is indeed how I’d recommend going about it. To avoid the “flicker” between image changes, you could copy the downloaded image to /tmp/newwallpaper.jpg (or something), switch to it then to your real path. Files in /tmp are deleted on reboots.

This is now fixed in the 4.0.3 b1091 pre-release  

Would it be possible to enhance the power pack clipboard feature to provide this as an option, possibly by holding an additional key, for pasting from the history?  If I'm not mistaken, using the template suggested above doesn't provide any history capability (which is the great feature of the power pack).

In the meantime you could use this AppleScript to send ESC to Alfred
 
on alfred_script(q)   tell application "Alfred 4" to activate   tell application "System Events" to key code 53 end alfred_script