To yell in game until it has been added back in to Procon.
Go to the Procon command console
You can't yell at a player only all players or a team.

admin.yell "then your message" Duration on screen <int>

Default duration is 10 seconds

Type:

All Players in game for 2 seconds
admin.yell "My Message" 2

All Players in game for 8 seconds
admin.yell "My Message" 8

U.S Army for 2 seconds
admin.yell "My Message" 2 team 1

Russian Army for 2 seconds
admin.yell "My Message" 2 team 2

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source of information...
http://www.phogue.net/forumvb/showthread.php?4149-Admins-New-Yell-Command-How-to