How to update under some condition

I have a system used by 8 clients, when something is changed in the system I put it on a server and when the client starts the system in his machine it updates from the server to the latest version.

My question is:

Is there any way to put some condition in this update? I would like just some clients update the system, not all of them.

Thanks

[383 byte] By [Franziska] at [2007-11-27 1:50:49]