Yep, we use the Haskell implementation as a library in Spago [0] and automatically migrating the configuration from old versions is a breeze as we can just manipulate the AST by pattern matching on it, e.g. see [1]
The above is quite standard in JSON/YAML too though, but an awesome thing you can do in Dhall is that - since you have functions - you can write migrations for Dhall data in Dhall itself, e.g. see [2]