All zabbix agent config parameters in the conf file can be overwritten by providing a new value later on in the config or (especially useful) in an included config under conf.d for example. This is very practical for automated installation systems where we don't want to edit the original config file but just to add and alter default configurations by appending new values at the end of the file or to included config files.
This approach doesn't work if you want to append a HostnameItem setting after a default config file presented a Hostname setting.