Flared Nostrils After Rhinoplasty- Is It Swelling?

It makes sense that as the tip projection is reduced during rhinoplasty that the nostril will tend to flare. It may not be swelling and a Weir procedure may be helpful to clean up your result. Wait a good while before deciding.
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If your tip projection was set back you will get some flaring of the nostrils. It's to early to tell how much versus the swelling though. If necessary nostril reduction can be done in 6-9 months as a minor touch up procedure.

While the shape, of the nose, can be altered by post op swelling after a Rhinoplasty, flared nostrils are not an area effected by this swelling IMHO.  This is more likely caused by manipulation of the tip cartilages and is something that you should discuss with your Rhinoplasty Surgeon.