[Zope] Appending to a file via manage_edit?

I've been looking around for this, but can't seem to find anything. I'm assuming that it is just not possible, but thought I'd ask just in case. For File objects, I see that manage_edit() has the parameters: title, content_type, precondition, filedata & REQUEST. Setting something in the filedata parameter will replace the file's current data with that. This implies (to me at least) that the only way one can edit a file is a complete rewrite. Does there exist a way to simply append data to the end of the file? For instance, if one wanted to write to a file line by line, is that possible in Zope? Thanks