I personally change the network settings manually with an editor, but I think
netconfig is the only text-mode tool to do this, so...
1) netconfig should have an option that it wouldn't rewrite /etc/resolv.conf.
This is needed on systems that want to use netconfig to configure non-primary interfaces.
You can avoid this by setting the correct DNS server for every interface, or not using TUI,
but a real solution might be in order.
2) netconfig should report if invalid options were input. That is, if you e.g. say:
netconfig -d eth1
Whoops! The correct syntax was -d=eth1 and netconfig just silently discards the option,
killing your current eth0 setup (and connection).
In a similar way, something like netconfig --uasdasvaslkdfvla doesn't give a complaint either..
Part 1) will probably continue to need to be done by editing files - putting a
PEERDNS=no checkbox into netconfig would overcomplicate it.
Part 2 should be fixed...