For some cases, a moderator might unlock and relock a post, however, I don't think that should be the case for this post and this type of edit.
From the FAQ you reference (emphasis mine):
Historically locking a post ends the debate over whether a question should be kept on the site or deleted, and is often the final state of a question that has been deleted and undeleted more than once.
So that is it. A locked post is locked, and will probably always remain what way (note that actively maintained posts shouldn't be locked, so this one wasn't maintained at least for some time). These posts will not be maintained any more, no matter how good your edit might have been.