For Yohanny Medina Herrera and many other youths living in America illegally, President Obama’s announcement yesterday that the federal government will allow young immigrants eligibility for work permits was a game-changer. But the new policy was especially significant for top-tier students like Herrera — young people who found that being valedictorian added biting irony to the legal limbo that prevented them from pursuing college or employment. “At least now it’ll be the beginning of something,” Herrera said.