In essence you are right…
However, Martin’s guide was written a long time ago and the standard Raspbian image has moved on to allow the wifi settings to be introduced to an image by adding a wpa_supplicant.conf file to the /boot partition before placing it into a Pi and that gets moved to the right location at boot up.
So to avoid the symlinkling being undone at first boot (the /boot copy moved into place deleting the symlink) you must use a different file name eg “wifi.conf”. See Wifi config on Pi Zero using emonSD and Using wpa_supplicant.conf file on the emonSD boot partition - #27 by bernamorillo discussions as this has been suggested, tried and tested before, but AFAIA not adopted on the emonSD image. It not only allows pre-configuration on a Pi, but in doing so it accommodates the Pi zero too, without impairing the existing emonSD setup (re RO OS and wifi module, untested on latest image)