You can reuse the child's configuration file in the parent and then add extra configurations in the parent package (e.g. you can have more than 1 configuration file in a package; if a value or property is set more than once, the latest setting wins).

The configurations will not filter down from parent to child. If you want this to happen, then you need to define configurations of the type "Parent Package Variable" in the child. The name of the variable does not have to be the same in both packages.