Hi rexi
 ... echo -e "#!/bin/sh\nexit 0" > exittc
chmod 775 exittc
sudo mv exittc /usr/local/bin/ ... 
I just tried this and it effectively disabled the  exittc  function.
Clicking on either  Exit  entry in the menu was silently ignored.
Clicking on the  Exit  icon was silently ignored.
Entering  exittc  on the command line was silently ignored.