I accidentally hit my nose 4 months post Rhinoplasty, can I have caused damage?

Though you are 4 months out, your nose is actually still healing, and will continue to do so for at least 12 months.  However, it is unlikely you caused any significant damage with this kind of injury.  The fact that you had no pain or bleeding is reassuring.  More importantly, though, is the appearance and function of your nose.  If the outward appearance has not been altered and you are still breathing well, you again are unlikely to have caused any harm.  When in doubt, contact your surgeon.

Trauma after rhinoplasty can change the appearance of your nose and affect your outcome, although thankfully this is rare.  A nose after a rhinoplasty requires time to heal.  Trauma can alter the shape of the nose, particularily if it is done prior to 6 months.  Avoid contact sports for 6 months and protect your nose.

He would take a significant blow to your nose in my opinion. The noise is pretty solid after four months. The fact that you have not had significant swelling, pain or a nosebleed would indicate my opinion that no significant damage was done. If you should however develop additional symptoms I would not hesitate to check with my plastic surgeon. Best wishes!