Can using a small cotton swab to clear mucus or sneezing through mouth loudly after a cold be harmful 6 weeks after rhinoplasty?

I would advise to clean your nostrils only with a solution and not with a cotton swab. I would get back in contact with your surgeon and ask for a solution recommendation. 

Thank you for sharing your concerns. I cannot speak for your surgeon. Though, most surgeon (me included) will allow rhinoplasty patients to gently blow the nose about 2 weeks after rhinoplasty surgery. We sometimes recommend the use of nasal saline sprays and rinses around the same time frame. Your best option is to call your surgeon's office. The office staff should be knowledgeable regarding your surgeon's specific restrictions on these types of activities.