Are corrective surgeries that "improve" one's appearance OK?

If someone has a surgery to fix a real problem and a side effect is that they look better afterwards, fine. This is what is called a "secondary effect," and is typically morally neutral if the primary effect is moral. Obviously someone's real motivation might be the secondary effect, rather than the primary treatment, but that's not for outsiders to adjudicate.

We do not recommend that people avoid surgeries that treat real problems just because they may also improve one's appearance. Hernia repair, some breast reductions, reconstructive work after injury or illness, repair for deviated septum, skin cancer treatment, etc. can all have a secondary effect of enhanced beauty, but have primary effects of restoring the health and function of the body.