Will making lifestyle changes matter if I have a genetic predisposition to being stressed?

Absolutely, yes! Many of us live in an environment with is predisposed to stress, with or without genetic predisposition. Lifestyle changes can make a huge difference. Start with the basics ("easy", but challenging to incorporate in to your daily schedule): eat a healthy meal/snack every 3-4 hours, go to bed relatively early and get enough sleep, try to limit caffeine and alcohol, and get up and move every day!