I've had 3 nasal polypectomy surgeries. i'm hoping the nasal polyps don't return this time. are there lifestyle or diet changes that can help prevent them from coming back?

Yes: If you suffer from recurrent nasal polyposis esp from allergic rhinitis then one thing you should definitely be doing is using a nasal steroid spray daily to prevent recurrence ie Flonase or its generic fluticasone for example. As far as diet and lifestyle you should avoid anything that triggers your allergies as well.

See allergist: Nasal polyps often inflammatory, often allergy related, not necessarily diet or food related. Allergy evaluation may be helpful.