Try This
<file name="admin/view/template/module/foo.tpl,admin/view/template/module/foo/foo.tpl">
<operation>
<search position="replace" offset="24"><![CDATA[
function file_upload(field, preview) {
]]></search>
<ignoreif><![CDATA[
function el_uploadSingle(
]]></ignoreif>
<add><![CDATA[
// new code for upload
]]></add>
</operation>
</file>