Set Static IP

[tkaiser]

Are you using SSH?

Yes

Then most probably nothing is 'bricked' but you lock yourself out. I still don't get which OS images you're using (since you said you want to deinstall the GUI and the original longsleep images are headless) but in case you've also the WiFi/BT module I would check with 'netstat -rn' how routes look like, disconnect the WiFi module if present and switch to non SSH mode (using keyboard/display or serial console).

The whole stuff is 'plain Debian' when you use longsleep's original Xenial image and it should be enough to change /etc/network/interfaces.d/eth0 the way you want.