Converting snapshots to layers

// 2016, use it at your own risk;

#target photoshop

if (app.documents.length > 0) {

var myDocument = app.activeDocument;

var thisHist = myDocument.activeHistoryState;

var theHist = myDocument.historyStates;

var theSnaps = new Array;

// create docs;

for (var m = 0; m < theHist.length; m++) {

var thisOne = theHist;

if (thisOne.snapshot == true) {

  myDocument.activeHistoryState = thisOne;

  var theName = thisOne.name;

  var theDup = duplicateImage (theName, true);

  theSnaps.push([activeDocument, theName, theDup]);

  app.activeDocument = myDocument;

  myDocument.activeHistoryState = thisHist;

  }

};

// duplicate layers;

for (var n = 0; n < theSnaps.length; n++) {

  var thisCopy = theSnaps[0];

  app.activeDocument = thisCopy;

  var theNewLayer = activeDocument.layers[0].duplicate(myDocument, ElementPlacement.PLACEATBEGINNING);

  thisCopy.close(SaveOptions.DONOTSAVECHANGES);

  theNewLayer.name = "snapshot_"+theSnaps[1]

  };

};

////// duplicate image //////

function duplicateImage (theName, merged) {

// =======================================================

var idDplc = charIDToTypeID( "Dplc" );

    var desc8 = new ActionDescriptor();

    var idnull = charIDToTypeID( "null" );

        var ref7 = new ActionReference();

        var idDcmn = charIDToTypeID( "Dcmn" );

        var idOrdn = charIDToTypeID( "Ordn" );

        var idFrst = charIDToTypeID( "Frst" );

        ref7.putEnumerated( idDcmn, idOrdn, idFrst );

    desc8.putReference( idnull, ref7 );

    var idNm = charIDToTypeID( "Nm  " );

    desc8.putString( idNm, theName );

    var idMrgd = charIDToTypeID( "Mrgd" );

    desc8.putBoolean( idMrgd, merged );

var theResult = executeAction( idDplc, desc8, DialogModes.NO );

// get doc ID;

var ref = new ActionReference();

ref.putEnumerated( charIDToTypeID("Dcmn"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );

var docDesc = executeActionGet(ref);

return docDesc.getInteger(stringIDToTypeID("documentID"))

};

I would recommend making flattened copies of the image at the various Snapshots and then collecting those as Layers into the original file.

For the beginning:

alert(activeDocument.historyStates.length);
alert(activeDocument.historyStates[0].snapshot); // if true, it's a snapshot

Have fun