The question was "how much will HRT affect facial appearance,..."?
Some seem to think that what I have said means that it is a "lost cause." I don't mean that at all. What I mean is that for a mature person, the change due to HRT will be limited. You should expect to have to work on other aspects of your feminine presentation.
Passing is very complex and I believe that we communicate our gender through body-language, voice, and mannerisms. On top of that we signal our gender through visual cues of clothes, jewelry, make-up, body-shape and , yes, facial features. My strategy has always been to use everything that I can easily change to communicate "I'm a girl!!" because there are things that I can't easily change.