function changeProductProperties() {
    $('single-view-product-itemnumberJS').set('text', $(this).getSelected().get('itemnumber'));
    $('single-view-product-priceJS').set('text', $(this).getSelected().get('price').toString().replace('.',','));    
}

window.addEvent('domready', function() {
    $('single-view-product-selectorJS').addEvent('change', changeProductProperties);
    $('single-view-product-selectorJS').fireEvent('change');
});