para eso existe la funcion
mc.swapDepths(otroMc);
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swapDepths (MovieClip.swapDepths method)
public swapDepths(target:Object) : Void
Swaps the stacking, or depth level (z-order), of this movie clip with the movie clip that is specified by the target parameter, or with the movie clip that currently occupies the depth level that is specified in the target parameter. Both movie clips must have the same parent movie clip. Swapping the depth level of movie clips has the effect of moving one movie clip in front of or behind the other. If a movie clip is tweening when this method is called, the tweening is stopped.
You can extend the methods and event handlers of the MovieClip class by creating a subclass.
Availability: ActionScript 1.0; Flash Player 5
Parameters
target:Object - This parameter can take one of two forms:
A Number that specifies the depth level where the movie clip is to be placed.
A String that specifies the movie clip instance whose depth is swapped with the movie clip for which the method is being applied. Both movie clips must have the same parent movie clip.
Example
The following example swaps the stacking order of two movie clip instances. Overlap two movie clip instances, called myMC1_mc and myMC2_mc, on the Stage and then add the following script to the parent Timeline:
Código PHP:
myMC1_mc.onRelease = function() {
this.swapDepths(myMC2_mc);
};
myMC2_mc.onRelease = function() {
this.swapDepths(myMC1_mc);
};
have funnnnnnn