You can edit the database file directly. In the tiki-preferences table, you can go to the sitemycode_publish row and remove the offending code.
> I have killed our Tiki instaltation by enting materials into the top banner area
> * ADMIN > ADMIN HOME > SITE IDENTITY > entering materials into the custom code
> * or on the ........tiki-admin.php?page=siteid page
> The result is that no page can be displayed.
> How can I get rid of the custom code so can regain control of our site.