is it possible to make everything "white" overprint?

I'll try the below methods and see if it will work correctly with our digital press.  Thank you for all your help!

OK, hang on a minute.

I think I've got this figured out, finally.

You're putting the white on top in the stack order, setting it to overprint so it isn't knocking out anything (nor is it being knocked out where other color is being printed because it's on top of the stack), but on press you are laying the spot white down first, which makes sense, and keeps it from obliteratiing all the stuff that's behind it in the .indd file. In that case the screen mode is perhaps unnecessary, though you may see some differences in color if there are areas of the art that overlap both white and raw metalic substrate.

I thought i saw a script on here a while back

This would set fills and strokes of page items (not text) to Overprint if the swatch name is "White"

var doc = app.activeDocument;
var api = doc.allPageItems;
var ws = doc.swatches.itemByName("White")
if (ws.isValid) {
	ws.properties = {model:ColorModel.SPOT}
} 

for (var i = 0; i < api.length; i++){
    try {
        if (api[i].fillColor == ws) {
            api[i].overprintFill = true;
        } 
        if (api[i].strokeColor == ws) {
            api[i].overprintStroke = true;
        } 
    }catch(e) {}  
};   

Are you using a spot color for White? That could be set to overprint, but I'm not really sure what effect you are after.

Can you explain what you are trying to achieve?

If your objects already have a swatch applied to them, this might be a solution.

In the swatches pallet, click on the dropdown menu in the top right corner.

choose "Find this color..."

Select the colour you want to change (probably "Paper" ?)

Select the color you want to change it to (this does not need to be a different color)

Then go to the "Object" tab, click inside of  the "Change Object Format" box.

The option dialog should open, choose the options you want to apply.

Then do a "Change All"

(you can lock / hide the layers that you don't want to change)

if there's a way to make everything in that layer overprint

Do you really mean everything—every fill and stroke of every page item and text characters?  With the exception of flattened grayscales and bitmaps, images can’t be set to overprint.

And by White do you mean a swatch named "White". A Layer named "White" could be set to not print in the Layer Options.

Is this for layers or objects and are you actually talking about overprinting white? Unless this is a very specific application that will result in nothing being printed at all.