Yes, that's what the code I gave you is intended to do....
you replace that code with whatever action you need to take to turn
your movie around.
I have no idea what your movieclip is doing, but I'm guessing
by your response that if it was an arrow pointing left to right
(just an example), you want it to be pointing right to left when
the left arrow is pressed. If you want an immediate turn around,
then the simplest way to do that is to have another frame
containing the movieclip that it moves to where it faces the other
direction--and to have it appear turned around, from the toolbar
you select Modify -> Transform -> Flip Horizontal.
So the movieclip would live inside another movieclip that has
two frames with stop()'s for each frame. In the first frame you
would have the subclip facing left to right, and in the second you
would have it facing right to left. If we call that 2-framed
movieclip "walker", the code I provided before would
become...