Check p. 59: Trait Vote, as well as Evolving Beliefs and Instincts. I personally think it's fine to alert your group to what you're angling for, but I don't feel like they're under any obligation to award you that trait. During trait voting, they nominate you for the one trait (character, call-on, die) that they think best personifies you. If you want them to award you a specific trait, you had better make sure that it best describes your character come vote time! Remember you get to nominate yourself for a trait as well--and the artha spent on Beliefs and Instincts are used as a guideline to the power of the trait.
So if you want that badass trait you couldn't afford, play toward it. Write Beliefs and Instincts that tie into it. Spend artha to accomplish them. When it comes time to vote, nominate yourself for it and defend it. It can also be useful if you don't rise quite to that point to go for a similar but lower-powered trait, especially a character trait. Show a progression.
On the mountains of truth you can never climb in vain: either you will reach a point higher up today, or you will be training your powers so that you will be able to climb higher tomorrow. -- Friedrich Nietzsche