by p. 186 of the core rule book, a warlord trait is "a preffered tactic or personal ability that marks them out amongst their peers." By that statement, I don't think you can grant the same trait to multiple characters. That said, you normally don't get more than 1 warlord trait for an army. In addition there is nothing that explicitly denies you from having 2+ characters with the same trait (with regard to this stratagem), but again you don't normally get more than 1 warlord.
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