It's been a little while since I've done some video work, but heres how I would do it
Code:
clip = ColorBars()
fr=30
clip.KenBurnsEffect(startFrame=0, endFrame=3*fr, endAlign=4, endZoomFactor=150).trim(0,3*fr)
last + clip.KenBurnsEffect(startFrame=3*fr, endFrame=6*fr, startAlign=4, startZoomFactor=150).trim(3*fr,0)
You do bring up an interesting point though, I might want to add a bool value that when set, returns the video back to its unmodified form after the effect is done. That would get rid of the trims at the end.