Comment 4 for bug 377519

An alternative fix would be for Launchpad's code hosting server to store the immutable database ID rather than the mutable string in the branch.conf file. This would require intercepting reads and writes to that file to transparently rewrite that setting (similar to how paths are translated on the fly when resolving paths to files/dirs on disk), and of course migrating the existing files.
This would have the advantage of working instantaneously, and it would not require changing a potentially large number of stacked branches in reaction to a single branch renaming.