I believe not. The system has given that flexibility to the user so that depending on the status of the returned materials, the user may wish to add it to the same lot/batch if it can be resold (provided he knows what it was) or may want to add a new/different lot/batch if it needs some other actions such as further inspections, repairs etc.
However, as a manual workaround, since the RMA line has the customer order no, line no and the delivery no, user can use this combination for the lot/batch no (which would not be ideal).
Also, if technically feasible, you may be able to have a custom field and have the customer order no, line no and the delivery no concatenated into this custom field so that the user can key it in (or have it populated directly) as the lot/batch no.
Hope this helps.