I actually mean in the user interface, where the client himself can edit the DNS records. He can only delete and add records, but not change existing records. E.g.: I want to change my MX record from:
mail.domain.com. IN MX 10
to
mail.domain2.com. IN MX 10
I now have to 1. delete the first and 2. add the second. Instead it would be easier to be able to edit the first entry.
No big issue ....