If the file you changed is a file xinetd uses as a configuration file, then you need to restart xinetd. I haven't messed with xinetd directly, so I don't honestly know, but it looks like it. Anyway, you can either use your system startup scripts to restart xinetd, or do it manually.
If your startup scripts file Red Hat's convention, then you should be able to execute something like this on the commandline:
The name of the script may be different; you'll just have to explore a little.
To restart it manually, you can use the kill command:
killall -HUP xinetd
The syntax may be different for your system. Do a man killall
to see. The SIGHUP signal forces the process to restart itself, causing it to re-read configuration files.
Otherwise, you can restart the machine.