Here is a tutorial on using A:M's "composite" feature to change individual light properties in a rendered animation without having to re-render the animation.
Many thanks to David Rogers and his excellent introduction to A:M Composite
http://www.hash.com/forums/index.php?showtopic=15282
More info can be found in this thread:
http://www.hash.com/forums/index.php?showforum=55