Is there a command for refreshing the Display Settings? Or, in specific, refreshing the Desktop Wallpaper?
You could try restarting
dock which, amongst many things, draws the wallpaper on the desktop. But be careful; as
dock also controls a lot of window management apps may 'un-minimise' or un-hide and windows. As
dock also controls Mission Control, you won't be able to change spaces or go into Mission Control until
dock restarts again (which is mostly instantly).
From terminal, try: