When you use
crontab or just type
select-editor you are presented with the list of the editors installed on the system. How do I add my custom editor to that list?
To add an additional alternative application to the Debian alternatives system, use
sudo update-alternatives --install link name path priority
To add an additional editor, run a command as:
sudo update-alternatives --install /usr/bin/editor editor /usr/bin/your-custom-editor 50
where the third entry after
--install is the executable of your custom editor. The first entry is the generic command that loads the selected editor, the second the name of the group of alternative applications. The number must be given and indicates a priority.
After that, you should be able to select your custom editor with either
sudo update-alternatives --config editor or
You can learn more about the Debian alternatives system here.