How can I keep my nostrils flared?

Injectable fillers may help.Botox certainly will not as it will give your the exact opposite of what you are after.

It's a good question.  Nostril flaring is a muscle action, so injections such as Botox will definitely not help, as the muscles relax when injected.It's possible that some judiciously placed filler may help, but I could not be certain of this in your case.Dropping the tip back with surgery will flare the nostrils in some.  You would need careful assessment.  See an experienced rhinoplasty surgeon and see exactly what is going on, and make your decision from there.All the best.

An effective, non-surgical way but time consuming, is to use dilating tube which can wither be silicone, rubber, metal, or even wood. You can adjust the size gradually as needed.

It might be possible to use botox or a filler first to try and achieve a flaring of the nostrils.
Surgery would result un a permanent scar so you should avoid this initially.