How can I lesson anxiety over not being able to breathe through nose after rhinoplasty?

The only way to mitigate that is to practice breathing through your mouth over the time span prior to your procedure. You can check with your surgeon to see if they will prescribe anti-anxiety medicine as well. Most patients can still breathe through their nose a small amount unless packing is used so you will have to discuss that with your surgeon. Good luck.

Packing is not always required after a rhinoplasty.  If needed there are splints that have a channel to allow for breathing after the procedure.  The problem is that these frequently get plugged by secretions.  Discuss your concerns with your plastic surgeon, you may find you are getting yourself worked up for no reason.  

Some surgeons will place a small amount of Kenalog injection in the head of the inferior turbinates to help prevent swelling and allow  some airflow. We do not place any packing inside the nose so most patients are able to get some  airflow through. Anti-anxiety medication such as  low dose Valium may also help