So - if you set the query field for the record you want, then query the main data source of the list form, you'll get back the record and can edit it. Your dropdown could be bound to the query ID field (you may have to put the data source task pane into advanced mode to see that) and have the list item ID for the value, and the title (or whatever makes sense) for the display. On change of the query field, execute the main data connection query. User can edit and resubmit. But, as I mentioned, I can't find a way to reset a form to "New" behavior after a query for an item has been run, so I'm not sure if the "switch to a different view to create a new item" feature is possible. I don't think it is.
Hilary Stoupa