MAC address randomization in Ubuntu 17+ (>= 1.4.1): save to /etc/NetworkManager/conf.d/

30-randomize-mac-address.conf

# /etc/NetworkManager/conf.d/30-randomize-mac-address.conf

# REQUIRES NETWORK MANAGER >= 1.4.1 (Ubuntu Zesty and above)

# Thanks to https://blogs.gnome.org/thaller/2016/08/26/mac-address-spoofing-in-networkmanager-1-4-0/

# This randomize your MAC address for *new* connections

# Be sure to change your existing (saved) connections in
# /etc/NetworkManager/system-connections/*

# NOTE: To support captive-portals that rely on a consistent mac address,
#       use `cloned-mac-address=stable` in /etc/NetworkManager/system-connections/[network name]

[device-mac-randomization]
# "yes" is already the default for scanning
wifi.scan-rand-mac-address=yes

[connection-mac-randomization]
ethernet.cloned-mac-address=stable
wifi.cloned-mac-address=random

# The options are:
#
# - permanent: use the hardware MAC
# - preserve: don’t change the MAC address of the device upon activation.
# - random: generate a randomized value upon each connect.
# - stable: generate a stable, hashed MAC address.
#

Hi Paul, coming here from your blog. I didn't quite understand how to do this part -

Be sure to change your existing (saved) connections in
/etc/NetworkManager/system-connections/*

So i followed your post and the suggestion from gnome's blog too, i.e made changes to the file in /usr/lib/NetworkManager/conf.d instead of directly editing the file in /etc/NetworkManager/conf.d. So far I haven't seen any changes in my mac address (same network) even after rebooting/ restarting network manager. Asked for help here by giving more details. Nothing so far.
Could you please elucidate how to do the quoted part above?