Apply overprint only to black objects & texts

Hi,

I am trying to write a script that apply Overprinting attribute to all objects & texts on all layers only to K=100.

I start from unlocking layers...

var doc = app.activeDocument;
for (i=0; i<doc.layers.length; i++)            doc.layers[i].locked = false;

By the way, is it possible to 'read' locked/unlocked state of the all layers by Javascript, perform some operations, and then lock back layers and leave unlocked ones as they were before performing the script?

Pete