How to rename a column family in HBase using HBase

Question

In the HBase shell, it's possible to delete a column family using:

alter 'tablename', NAME => 'familyname', METHOD => 'delete'

It's also possible to create a new column family using:

alter 'tablename', NAME => 'newfamilyname'

So it's possible to delete a column family and create a new one, but if I have existing data, deleting the column family deletes the data within that family as well.

How do I rename an HBase column family in an existing table without losing the existing data?