De http://dev.mysql.com/doc/refman/5.0/es/date-and-time-functions.html
Para "sumar" un día a fecha_registro
:
mysql> SELECT '2013-05-31' + INTERVAL 1 DAY;
+-------------------------------+
| '2013-05-31' + INTERVAL 1 DAY |
+-------------------------------+
| 2013-06-01 |