$(document).ready(function() {
    var $select = $('#select');
    var $custom = $('#custom');
    var $customValue = 'Другое';

    $select.on('change', function() {
$name =  $(this).val();
       if ( ($this).val() == $customValue) && ($custom.val() != '') ) {
         $(this).val() = $custom.val();
        }
else {
$(this).val() = $name;
}
    });
});