@classmethod
def set_class_default(mcs, model, attr, value, instances=False):
    """Set DEFAULT attribute for Model class

        Arguments:
        model -- name of model class
        attr -- attribute name
        value -- new attribute value


        Keyword arguments:
        instances -- update instances too (default=False)
        """
    cls = mcs.__classes__[model]
    if attr in cls.REPLACE:
        attr = cls.REPLACE[attr]
    if attr in cls.DEFAULT:
        cls.DEFAULT[attr] = value
    if instances:
        cls.set_instances_default(attr, value)
