[quote=@ToadRopes]
[@Silver Fox]You'll be able to start customizing your Trainer after Hau'oli City, and I think haircuts come on the island after Melemele.
[/quote]

There are some haircuts in Hau'oli, as well as outfits, but they're pretty limited.  At least, I hope there are more than four haircuts in the game for dudes.