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.