YAML has its detractors and many of the criticisms against it are valid. It’s ambiguous and confusing and deeply nested significant white space, with odd indentation rules and optional syntax, is incredibly hard to follow as a human.
Given some YAML file, making any kind of automated change generally nukes the formatting entirely, let alone the comments. I'm sure there are some libraries that do it right, but there seem to be far more that are just awful.
One nice thing about Dhall is that there's a reference implementation written in Haskell where they have very good pretty printing libraries so it's likely that programs would be able to do automated updates to configuration.
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]
[0]: https://github.com/spacchetti/spago [1]: https://github.com/spacchetti/spago/blob/a77b869edcfddd592f4... [2]: http://www.haskellforall.com/2017/11/semantic-integrity-chec...