Update Dock after defaults write without `killall` restart
Send the Dock process a signal called the 'hang-up' or HUP, also known as signal number 1 as defined somewhere in a system signals.h header file.  POSIX convention, I believe.

The quick and dirty:

sudo pkill -1 Dock


What a HUP signal should effectuate in the receiving process is an internal halt and re-evaluation, which usually includes a re-reading of any relevant config files.  The process will not terminate, only 'refresh' itself.

Hope this helps.

F.