csrutil disable
Restart computer
In the terminal, type
sudo open /Applications/TextEdit.app /System/Library/LaunchDaemons/com.apple.ManagedClient.enroll.plist
change
<key>com.apple.ManagedClient.enroll</key>
<true/>
to
<key>com.apple.ManagedClient.enroll</key>
<false/>
So that the changes take effect
It should not matter; You do not need to change it.
0.0.0.0 might be better because the system would interpret it as a completely invalid non-routable address while 127.0.0.1 would have connections back to the local host loopback thus getting a reply, socket closed. If I was actually running a web service hosted on my machine and it was bound to the adapter, programs would actually hit my own web server when using 127.0.0.1/8.
There is an "easy" console text editor included in MacOS called "nano". In order to modify a system-wide configuration file in /etc, you will need Administrative permissions (root). You gain this access with the sudo command. For example,
sudo nano /etc/hosts
Use the arrow keys and keyboard to edit the file, press CTRL+X to exit, press Y and then [ENTER] to Save when prompted.
Theoretically Yes, but I have not tested or checked on what protections (if any) are done during the setup process. I also do not have any recent Mac to test on. Editing the hosts file may be similar but the mount paths are likely to be different; you may need to manually mount data volumes. In Install/Recovery mode, you are already root, so sudo is not needed; I am unsure is nano is included. Worst case would be to use vi instead.