Ubuntu 18.04.3 netboot PXE fresh installed boots up with Ethernet not managed by Network Manager

I'm trying to set up a **PXE** server to deliver Linux image for end user workstation in my company. I've finally made it to set up dnsmasq and nfs-kernel-server so now I can get the images via network and start the installer. *The problem is*: all installer steps runs well but when I get into my fresh installed OS the Ethernet connection appears as "**unmanaged**" by Network Manager. Looking for an answer to it on the web I've realized there's a workaround that solves the issue. *My big doubt is*: Is there a way to preset an post-install config file (/etc/NetworkManager/NetworkManager.conf) inside ISO's folder to prevent this behavior? **NOTE**: installing the same ISO from a flash drive prevents the problem, but I don't understand this behavior because both PXE server and flash drive are using same initrd and vmlinuz files. Could anyone please give me a hand? Thanks in advance.