Replication Server 15.2 includes the set template to option for the alter error class command.
alter error class error_class set template to template_error_class
alter error class my_error_class set template to rs_sqlserver_error_class
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. See the Replication Server Reference Manual.