When using extended smarty output, the following code illustrates how the
smarty-variables could be used when dropped into the entries.tpl:
{if isset($entry.freetag.extended) && $entry.freetag.extended == 1}
{if $entry.freetag.tags.tags}
{$entry.freetag.tags.description}
{foreach from=$entry.freetag.tags.tags item="tag"}
{$tag}
{/foreach}
{if $is_single_entry or $is_preview}
{$entry.freetag.related.description}
{/if}
{/if}
{else}
{$entry.freetag}
{/if}
Using this subquery you can convert existing categories to tags:
INSERT INTO serendipity_entrytags (entryid, tag)
SELECT serendipity_entries.id, serendipity_category.category_name
FROM serendipity_entries, serendipity_category, serendipity_entrycat
WHERE serendipity_entrycat.entryid = serendipity_entries.id
AND serendipity_category.categoryid = serendipity_entrycat.categoryid;
[quoted from: http://pixelated-dreams.com/archives/229-Spring-Cleaning.html]
Or using this script you can convert existing categories to tags:
\n",
htmlspecialchars($row['category_name']),
(int)$row['id'],
htmlspecialchars($row['title'])
);
}