Help organizing dozens of layers with hundreds of sub-layers.

Yes, the line patterns stay the same for each of the grades.

ok. I read that.. but it doesn't answer any of my questions. 

let's say you run the script. it starts on layer 1.. what should it name layer 1? How does the script know how to make a decision? An example answer to this question is this: "i have a spreadsheet with values input in the same order as the layers i want to rename. the first value in the spreadsheet should be used as the name for layer 1. second value for layer 2. etc". Or perhaps an answer could look like this: "there's a text frame inside each layer that contains the text i want to use for the parent layer name."

Moving beyond that, when you get to the items inside each layer, the same question applies. You mentioned that you have a bunch of items called "<path>".. this means they're unnamed and can't be accessed by name. So, if we just loop through all of the pageItems on a given layer, how do we know what any of them should be called? If the script reaches a pathItem inside layer 1, how do you know whether that path represents the front,back,collar, etc?

Scripts are great and they can definitely give you the efficiency boost you're looking for. But they can't read your mind. In order to write a functioning script, we need to know what the inputs are and what the outputs should be. We need to know what the rules are so that we can determine how to structure the code to do the thing that you want to do.

on a fundamental level, the answer to your question is this:

//to rename a layer
app.activeDocument.layers[0].name = "New Layer Name";

//to rename a pathItem (or any pageItem)
app.activeDocument.pathItems[0].name = "New Path Name";

//to move a pageItem from one layer to another
//this moves the first pathItem in the document to the second layer in the document
app.activeDocument.pathItems[0].moveToBeginning(app.activeDocument.layers[1])

As you can see, it's quite easy to change the name of something. But the value that you change it to needs to come from somewhere.

So, assuming you were doing this manually, when you opened a layer and found an unnamed path that represents the "front" of a garment, you'd double click on the item in the layers panel and type the new name, correct? So what is the decision structure that leads you to deciding to call that piece "front"? Is it just that you can look at it and recognize it as a "front"? Or are the pieces stacked in order in some way so that you're always changing the first item to "front" and the second item to "back" and the third item to "left sleeve" and so on?