Re: GUIDs or other stable names for pages, via REST
No. Or at least what we call "page name" in XWiki what you have in the
URL and is part of the id of that page on the database side too.
That said when you rename a page in the UI a "redirect" (it's actually
closer to a simlink than an http redirect) is created when the page
used to be.
Also the title and the page name are technically two different things
and what you see in the UI is usually the title so it's possible to
change the display name without changing the actual reference