There is no upgrade that any free hosted WordPress.com blogger can purchase to allow access to the metadata files and editing of them. WordPress.com users do not have access to the database files and cannot edit the templates containing the HTML and php underlying their themes. At WordPress.com all users are working on the same wpMU ( WordPress multi-user) blogging platform, and are all sharing the same templates. As any editing would affect all blogs wearing the same theme, so only Staff have access the files and are able to edit them. Every edit made affects all blog wearing the same theme.