Syntax:
ALTER FUNCTION func_name [characteristic ...]

characteristic:
    { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
  | SQL SECURITY { DEFINER | INVOKER }
  | COMMENT 'string'

This statement can be used to change the characteristics of a stored
function. More than one change may be specified in an ALTER FUNCTION
statement. However, you cannot change the parameters or body of a
stored function using this statement; to make such changes, you must
drop and re-create the function using DROP FUNCTION and CREATE
FUNCTION.

As of MySQL 5.0.3, you must have the ALTER ROUTINE privilege for the
function. (That privilege is granted automatically to the function
creator.) If binary logging is enabled, the ALTER FUNCTION statement
might also require the SUPER privilege, as described in
http://dev.mysql.com/doc/refman/5.0/en/stored-programs-logging.html.

URL: http://dev.mysql.com/doc/refman/5.0/en/alter-function.html

