Is it feasible to repair the upper of a shoe?

There's some pics of the Prince of England wearing shoes with repaired uppers. But I believe those are custom Lobbs he wears. Unless your shoes are especially precious to you or extraordinarily expensive I doubt it would be worth it. I don't know of anyone who would do such work.

Creases aren't damage. They're the natural consequence of wearing the shoe. Not sure what you mean by dents. Certainly you can prevent creases from turning into cracks with shoe trees and regular polish and conditioning, but they're never going to go away entirely.

As for patching holes, it is possible, but hard and thus expensive. Unless you're wearing custom shoes and are just too stubborn to let them die, I wouldn't bother.

Anyway, here's the pic of Prince Charles' shoes. Yes, it's possible, if you have a beloved pair of 40 year old bespoke shoes.