Systemd services are configured with a .service file, which is a text file (but not a shell script). I don't know why the author made the bizarre suggestion th

Systemd services are configured with a .service file, which is a text file (but not a shell script). I don't know why the author made the bizarre suggestion that anybody would start tinkering with the source of systemd itself in order to configure services, and it would be impolite to speculate. Suffice to say that nobody does this. Certainly you can take advantage of more systemd features by modifying the source of the service to explicitly support them; however, this is not something users/sysadmins should ever need to do themselves.