Joined: 14 Mar 2007 Posts: 8657 Location: Back in jolly old England
Yes, it is possible.
You will need to modify the logon procedures to do this, and this will affect every user that uses the same proc(s).
Why would you want to display such a message anyway - everyone knows that TSO runs under z/OS anyway. And if they don not know then they should not be trusted to have access to a logon in the first place.