I have made it work. See my example code:
add_filter('acf/load_value/name=product_type', 'my_acf_load_value', 10, 3);
function my_acf_load_value( $field ) {
if (isset($_GET['product_type'])) {
$product_type = $_GET['product_type'];
$field = $product_type;
}
return $field;
}