there is an yang,
now I need to change the name of key (leaf kii) to something else.
is there any tail-f statement from which I can achieve the above or any solution for that?
When you change the YANG model, e.g. the name of the key for a list, you change the database schema. So you need to do that through an upgrade. See the ConfD UG’s CDB chapter and the In-service data model upgrade chapter.