If you will update the DNS of your website that means currently your website is working from one server and now you are updating the records so it will start working from other provider's server. That is your are moving your website from one provider's server to another web server.
Definitely, it will affect the traffic and SERP as during DNS updating the site goes down for some hours due to DNS propagation. DNS used to take 4 to 8 hours to propagate over the internet. So it's always recommended to update the DNS when there is less traffic in off-business hours that is in mid-night.
I will suggest you to update the DNS during the off-peak hours.
Hope this answer will help you. :)