Use the alter error class command, and another error class as a template, to alter error classes. alter error class copies error actions from the template error class to the error class you want to alter and overwrites error actions that have the same error code
alter error class error_class set template to template_error_class
For example, to alter my_error_class for an Oracle database based on rs_sqlserver_error_class as a template:
alter error class my_error_class set template to rs_sqlserver_error_class
