Dear John,
There is no way to retroactively change the name of all instances of an actor in existing stories.
While it may seem like an obvious bug at first, it is actually a bit more subtle than that.
Indeed, the actor name is part of the story statement, which is often critical and carefully crafted by a human. Having a hard link so that the actor name change is automatically reflected everywhere is too radical. Indeed, when renaming an actor, you may just want upcoming stories to be affected by the change and not the one belonging to past sprints. Changing past stories indiscriminately could break the trust you have than when you write something, it stays as you wrote it unless you actively want to change it. That is why we decided to loosely couple the actor name so the hard link is made only on the ID.
In this case, automatic renaming should be provided as an option. However, a consequence of the loose link is that it that such automation is harder to implement, so with an agile mindset we decided to start without it and see if the need would arise. Until now we received very little feedback as the need to rename actors seldom occur and when it occurs, it is mainly at the very beginning of a project where changing the name manually on each story is quite inexpensive.
Anyway, your feedback is valuable for us and if we notice more interest for automatic renaming then we may implement it.