Why we probably won't ever see a name change service...

[Bixby]

I've been looking all over the place for something on that matter and wasn't finding it. Thanks for letting me know.

Here's the post where they talk about it being temporary.

And then there's this:

As mentioned in this thread, the team is still discussing the details around this, but in the future we definitely want to offer more phials of Fantasia as well as something that allows players to change their name.