Is there a way to control the submit so that file name is generated for a
new form, but uses the current file name if the form already exists in the
document library?

I have a form that multiple users will update in a SharePoint document
library.  Currently my Data Connection that does the Submit generates the
file name using the current time.  This works great the first time a form is
submitted, but the second time the form is edited, it creates a new form in
the library with a new name.

I am trying to do this with just rules so I do not have to create custom
code for every form that needs this behavior.