[Zope] Can't customize scripts in CMF/plone

Zope-2.5.1-x86, CMF-1.3beta, CMFPlone-0.9.9 I'm trying to customize the plone search form. If I "Customize" portal_skins/generic/search, then I get this error when I do a search: Site Error: Error Value portal_url not found in 'portal_url', at line 25, column 13 That error is in standard_html_header. Then, I tried customizing portal_skins/custom/doFormSearch, but non of my changes had any affect. I think the customize method only works for page templates, but is broken for scripts and portal tools. Am I missing something?