Note: if you add the exec from the video into your .login to change the default shell on myth, you won't be able to physically log in to the linux cluster computers (myth, corn, pup). You will still be able to ssh into them. If you need to physically login but already made the change, then you should click on "session" and load a failsafe terminal, then run the command "gnome-session" at the terminal.
If you want it to not crash, instead use the following exec line in your .login:
if ( $?prompt && -f /bin/zsh) exec /bin/zsh -l
$?prompt checks if the prompt is defined. In other words, if the shell is actually interactive, then execute zsh as the login shell.
In order to make your terminal use zsh instead of tcsh, you need to make sure that it starts as a login shell. There should be an option to do that in the terminal graphical user interface's preferences