Courts should invalidate any welfare definition change that seems too directly an attempt to favor a specific policy whose main rationale comes from other measurable
outcomes
That - and your "miles of road" example - seems to me to invalidate changing the welfare definition to add welfare weightings for tax levels.
Putting in weights to directly favor specific policy proposals is very different from putting in weights to penalize the kinds of means that people dislike. For example, if we dislike police detaining folks without charging them with a crime, we could count such events and penalize them.
Courts should invalidate any welfare definition change that seems too directly an attempt to favor a specific policy whose main rationale comes from other measurable outcomes
That - and your "miles of road" example - seems to me to invalidate changing the welfare definition to add welfare weightings for tax levels.