Currently not built in. It's not hard to load an image in (1 line of code, I think), but there are no mechanisms today for overriding what an actor's animation/image is.
Roughly, what you'd need to do is load the image (which gets you a BitmapData) and then in a drawing event, call g.drawImage(img, xPos, yPos). Not literally that code, but that's the approach you'd need to take.
You'd also want to call "hide sprite" on the actor to stop its regular drawing.