For open networks which do not require a password, omit the WIFI_PASS option.
To disconnect the Key Croc from a network, remove the WIFI_SSID and WIFI_PASS options, then restart the device.
By default the Key Croc is configured to attempt to obtain an IP address from a network's DHCP server. Configuring a static IP address is outside the scope of this guide, however considering its Debian base this can be achieved in a number of ways.
The DNS server may be overridden from that obtained via DHCP by using the DNS option in config.txt, in the format:
DNS x.x.x.x x.x.x.x
To determine the IP address obtained by the Key Croc for development purposes, see the guide on Interactive Payload Development from the Tips section of this documentation.