[Solved]-Add Source to Highcharts Export CSV-Highcharts

You could extend Highcharts and wrap the getCSV function, or edit what happens when you click the Download CSV menu item.

An example of editing what happens when you click the menu item (JSFiddle):

menuItems: [{
    textKey: 'downloadCSV',
    onclick: function () {
        var csv = this.getCSV(true);
        csv += '\n"My source 1","My source 2","My source 3"';
        this.fileDownload(
            'data:text/csv,\uFEFF' + encodeURIComponent(csv),
            'csv',
            csv,
            'text/csv'
        );
    }
}]

An example of extending Highcharts (JSFiddle):

(function (H) {
    H.wrap(H.Chart.prototype, 'getCSV', function (proceed, useLocalDecimalPoint) {
        // Run the original proceed method
        result = proceed.apply(this, Array.prototype.slice.call(arguments, 1));
        result += '\n"My source 1","My source 2","My source 3"';
        return result;
    });
}(Highcharts));