Can GuestEntries edit existing entries? I'm trying to use &lt;input type="hidden" name="entryId" value="{{entry.id}}"&gt; on a GuestEntries form. However, instead of editing the entry with the set ID, it creates a new post. 

Am I missing something? Or is this not possible with the GuestEntries plugin.
Correct. It currently only allows for creating new entries, not editing existing ones.