"Replace with Precomp" Script

Hi Everyone, I found a different solution:

1- assign the layer of a comp you want replaced to a layer to a variable.

2 - assign the comp you want to replace the old comp to a variable.

3 - get both vars to be var.selected = true;

This will select the old comp layer and the new comp that will replace it.

Then you do  as @foxbot1979  mentioned, 

var1.replaceSource(var2.true)

This emulates the alt drag that you usually have to do manually.

Hope it helps!

Not that I know of natively. It could be coded though.

On pg. 47 of the After-Effects-CS6-Scripting-Guide.pdf you can replace a layer with another AVItem object.

app.project.item(index).layer(index).replaceSource(newSource, fixExpressions);

//START

var myComp = app.project.item(1);     //Assuming your active comp was the 1st item in the project panel.

var layerToReplace = myComp.layer(1);     //Assuming the layer you are replacing is layer 1.

var newLayer = app.project.item(2);     //Assuming your replacement layer is the 2nd item in the project panel.

layerToReplace.replaceSource(newLayer, true);

//END