So, I'm wondering if it's possible to stop all animation, do computations such as "moving a bunch of enemies movieclips, moving some bullets, etc.", then starting the animation again so that all of the drawing would occur at once. 

My application would be in the game loop of my game. The problem I'm having is that I have around 50 enemies on screen, all of which are moving very fast, and I walk through the array and move each MovieClip. There's some lag and I'd like to get rid of it in any way I can.

If I understand AS3 correctly, it would try to draw to the screen after each change of the X and Y value of each MovieClip. By stopping animation, setting these values, then starting it up again, I think I'd increase performance by quite a bit.