Changing multiple individual posts to wide with no sidebar en mass?

I just started using Catch Box Pro on a pre-existing site. On the first page of the site I have a right side bar. For new posts, I know I can chose wide with no side bar. I have 5000+ pre-existing posts that I would also like to appear on a wide page with no side bar. Is there a way to do this in mass via a piece of code? Having to go to every post and choose wide with no sidebar is going o be a lot of work and take forever. Thank you