Hi-
Save and Submit are different operations, so let's clarify.
Save allows the user to enter a filename.
Submit executes a data connection to perform the submit operation, and this includes a pre-defined filename.
You can dynamically generate a filename via rules in your form. Your form can also have many different submit data connections, and only execute one of them - perhaps you can find a way of determining where the form was opened from and based on that information execute a different submit data connection.