What can moves bones after rhinoplasty?

I've never heard of hard sniffing or heavy breathing causing the nasal bones to shift after rhinoplasty.You should contact with your surgeon regarding your congestion concerns. It's expected to have congestion initially after rhinoplasty.

during a rhinoplasty, the force required to move bones is much much greater than the forces generated during sniffing, sneezing and any other normal day to day activity

Trauma to the nose will move bones after surgery.  When the splint is off, that is when you should use extreme caution.  Heavy breathing and sniffing will not move the bones.  Your airway feels congested because you have swelling on the inside of the nose as well as the outside.  Follow up with your surgeon for an exam.