Thanks Antek, the resource you linked is very helpful.
I also found an interesting answer on the topic on Unix StackExchange => unix.stackexchange.com/a/271991/41613
In the end I managed to disable the WiFi button by creating a file /etc/hotplug.d/button/50-wifiswitch with this code inside:
#/bin/sh
if [ "$BUTTON" = "rfkill" ] ; then
if [ "$ACTION" = "released" ] ; then
logger "Ignoring disable wifi (rfkill button released)"
uci set 'wireless.@wifi-device[0].disabled=0'
elif [ "$ACTION" = "pressed" ] ; then
logger "Enabling wifi (rfkill button pressed)"
uci set 'wireless.@wifi-device[0].disabled=0'
else
logger "Unknown action: $ACTION"
exit 1
fi
wifi
fi
Hopefully this will help my clumsy clients ;-)
Note however this solution relies on hotplug, which as far as I understand is being phased out. Alas I don't know how to adapt it to procd.
Cheers,
Guido