1st page in the Event Commands, "Face Graphics". Use that to change the current face that's displayed. Note that it'll keep that face until you tell it to change/erase it.

Basically, like this:

<> Change face to Alex
<> Message: "Alex: Blah blah"
<> Message: "Alex: Random story thing"
<> Change face to King's face
<> Message: "King: Fetch me a twig"
<> Change face to blank
<> Message: "You got: \c[3]Twig Permit\c[0]!"
<> Change items: Add 1 twig permit
<>

..Though it won't use things like "King's Face", it'll use the faceset name and the position of the face on the faceset, but you get the idea.