How do I change values of LAB colors in Illustrator using a script?

I am trying to write a script in JS, that will run through all the objects in my file, and change their LAB color values (change L individually, A, and B).

I tried this code:

var doc = app.activeDocument;
doc.swatches.getByName("MySwatchName").color.l = 42;
doc.swatches.getByName("MySwatchName").color.a = 40;
doc.swatches.getByName("MySwatchName").color.b = 2;

But it doesn't work. Changing the name of the swatch was possible, but not changing the color values.

I read this article and now I wonder, might it be that what I am trying to do is impossible with the scripting API?

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