Change Welcome message to display First Name only without changing any other display options

My company would like a more informal welcome message for people logging into the system. Instead of the current "Good afternoon Peter Smith!" we woud like to display the more friendly text "Good afternoon Peter!" (see attached screenshot)

I was only able to do this by changing thee display name format to do this but this also impacts on other displays like the search list or notifications which we do not want to change.

Is there any way of updating the Welcome message as displayed below without impacting anything else?