/etc is just a symlink to /private/etc, so they're the same configuration
If I were you, I would just edit that file, uncomment the "#Port 22" line, and add another line after it with "Port 2222" or whatever other port you want. SSH will then listen on both. You'll need to restart the daemon (easiest way would be to just uncheck it in Sharing and recheck it). Of course, you'll need to add access through to port 2222 in your firewall configuration as well.