To begin migrating your data start with a type family for your record and index it with a natural number

    data family Foo (version :: Nat)

    newtype MyString = MyString { unMyString :: String }
       deriving (IsString, Show, Eq)

    data instance Foo 0
      = FooV0
        { _fooId :: Int
        , _fooName :: String
        }
      deriving (Generic, Show, Eq)

    data instance Foo 1
      = FooV1
      { _fooId        :: Int
      , _fooName      :: MyString
      , _fooHonorific :: String
      }
      deriving (Generic, Show, Eq)

    instance Transform Foo 0 where
      up   v = genericUp   v (const "esquire") (const MyString)
      down v = genericDown v (const unMyString)

You provide an instance of the Transform class for your type in order to specify how to transform version n to version n + 1 and back.

Presently only simple record types are supported. More to come in the future.