Sets all existing wifi networks' cloned-mac-address to preserve, the previous default, if they didn't have one set already.

setoldnmdefault.sh

#!/bin/bash

for nmprofile in /etc/NetworkManager/system-connections/*; do
    # check if a cloned mac was already set
    if grep -q "cloned-mac-address" "$nmprofile"; then
        echo "$(basename "$nmprofile") already has a cloned mac address. No changes."
    else
        # If it doesn't have a [wifi] section, it's not a wifi network
        if grep -q "\[wifi\]" "$nmprofile"; then
            sed -i '/\[wifi\]/a cloned-mac-address=preserve' "$nmprofile"
            echo "Set cloned-mac-address=preserve in $(basename "$nmprofile") profile."
        else
            echo "$(basename "$nmprofile") isn't a wifi network. No changes."
        fi
    fi
done