I'm currently running Sendmail version 8.11.6 on my server. I was wondering if it was possible to create a script to have sendmail read the local-host-names file and process it without having to restart sendmail. I'm just trying to figure out a way to do it without disturbing anyone when I have to reboot.

Not sure if this is what you mean, but you dont have to restart the computer to restart sendmail. if you make changes to most files related to sendmail they wont take effect until you restart sendmail. Restarting sendmail only takes seconds though, so if you do it at a time when mail traffic is slow, there wont be any disruption of service.
There are many ways to do this depending on the distro you are using.
Most of the time you can (as root) kill sendmail and restart it using the rc.sendmail file.

Sorry I wasn't more specific, but yes I was wondering if there was a way to do it without stopping and restarting the sendmail service. Some kind of perl script maybe? Or is it not likely because the local-host-names file is a text file.
Thanks for the help

After reviewing how the local-host-names file is setup, it doesnt look like sendmail would need to be restarted. Also there doesnt seem to be a script to update it to a .db file like the alias file has. If your sendmail.cf is set up correctly (which it is by default im pretty sure) then it will read that file every time there is a request for a mail connection.
Have you tryed adding entries and tested them? (sorry if that sounds insulting-not intended)
In the meantime, I will add some things to my file and test it myself to see the functionality.

Having problems with my dns server. Ill work on that and try again later. ill check back later.

Thank you, I'll try in the morning and see what happens. After that I'll immediately post my results.