Paul Jones has posted an article to his site with another helpful hint to modernize your legacy PHP application. In the post he looks at updating serialized object handling with the help of the class_alias function.
Several weeks ago, a correspondent presented a legacy situation that I've never had to deal with. He was working his way through Modernizing Legacy Applications in PHP, and realized the codebase was storing serialized PHP objects in a database. He couldn't refactor the class names without seriously breaking the application. [...] Before I was able to reply, my correspondent ended up changing the serialization strategy to use JSON, which was a rather large change. It ended up well, but it turns out there is a less intrusive solution: class_alias().
He talks about how this function could be useful to prevent the need for updating the class name in every serialized instance by setting up an alias to the new name. You can even use namespacing in the alias that will let the autoloader work with the PSR-0/PSR-4 handling to correctly load the class. With this in place, you can then refactor to the new version of the class without worry of breakage.