Make a copy of the file
"C:\Users\XxxX\Documents\My Games\RedOrchestra2\ROGame\Config\ROInput.ini" before trying this in case something goes wrong, i tested myself the teamsay one, binding it on numeric pad key 9 and it works.
In console (F3) enter this command ( copy and paste with Ctrl+V works in game console btw):
Setbind NumPadNine "Say Acknowledged"
Setbind NumPadNine "TeamSay Acknowledged"
Setbind NumPadNine "SquadSay Acknowledged"
Choose the one you want ( 1st is chat for all , 2nd team only, 3rd Squad only ) , i think you want the team say one, but i put others just in case anyone needs them too .
Numeric pad keys seems to be a good choice as they don't seems used by the game ( NumPadZero to NumPadNine ) but you can replace by any other key not used by the game itself too.