It is possible the imps episode is an intrusion from another ballad on the same theme of the early 19th century (may be slightly older) called 'The Devil In Search of A Wife'. In this the Devil goes to London where he goes into a party. The women give him short shrift but he eventually carries one off, then we get the detailed description of how she mistreats the imps and their pleading with him to take her back as in 'The Farmer's Curst Wife'.

As with many ballads I think oral tradition has done us a lot of favours.