I found this solution which allows to save the setup and makes it visible in the OS X Network Preferences:
a) Loopback device in System Preferences visible
$ sudo networksetup -createnetworkservice Loopback lo0
b) setup the ip
$ sudo networksetup -setmanual Loopback 172.16.123.1 255.255.255.0
Use case: debugging php server with Xdebug Client on MacOS