It's not currently possible to edit the path (on the old site) for a mapping, no - once a mapping is created it's there for good. Your [commit message](https://github.com/alphagov/transition/commit/bb46f03fe037a7982898bd73e9c36e984d99a94b) says 'Current assumption that mappings source paths are immutable' - I just noticed that that comment seemed to contradict the commit message.