Restart on if something changed?

[PAUL WILLIAMSON]

How can I tell a process to restart only if a certain file has changed?

We just changed the way our login banners are supposed to occur.
Before, they appeared prior to login, so I could just use the 
sshd_config file and specify an banner in the file.  Now, I need 
to present the banner after login.  In order to do this, I need to 
restart sshd.  But, I don't want to restart sshd during the 
middle of the day or when the sshd_config file hasn't changed.

Paul