In Mistborn, can Allomancers burn zinc and brass to Riot or Soothe their own emotions, such as to calm down if scared or cause a fight-or-flight reaction to trigger adrenaline?
No, they are explicitly stated not to be able to:
He knew himself a fool. However, he could not help how he felt. One could not use emotional Allomancy on one’s self
The Well of Ascension chapter 46, page 578 (2014 trade paperback edition)