Just some additional hints and ideas...
One way to achieve this with inheritance to child docs (as well as the ability to override the value for each child), is to use a Template Variable with the default value of @INHERIT, then set the value on each top level container document to the actual alias.
Or, you could also just use the GetField snippet in conjunction with the UltimateParent snippet to get the top level parent’s alias no matter where you are in the document tree.
The latter might be the better choice here, as you can use cached snippet calls in conjunction with the partial page caching MODx provides to reduce the overhead (as compared to having a TV parsed in the template each time).
My point is simply, there are a lot of ways to do things like this in MODx; finding the best approach to a problem/requirement can be the biggest challenge, and the most fun.