Oh, I guess it is! That's bad, would love some more details on how you did it.
Oh, I thought you had found a way to reassign posts to different users, but it looks like you only changed your display name to "Sacha Greif"? That's less severe.
We could check for display name uniqueness, but then you'll never be able to prevent people from using special characters, etc. to fake other names. So I don't know if it's worth going down that route…? Still, I would accept a PR for this.