I think that depends on the strength and skill of your allomancy, and how invested the heralds are at the moment, as invested being are harder to affect with emotional allomancy. I’d guess if the lord ruler duralumin pushed his zinc/brass he’d be able to effect a herald, although I’m not sure.
As for the usefulness of this, he could perhaps weaken taln’s mental state further, driving him to collapse, although that’s probably implausible.