Quick question about Google Analytics and FB Pixel over migrating a New WP install

Hi, this is really playing games with my mind, since I don't exactly remember all the custom code I added into my original WP site, so the situation is:

I want to completely build a 2021adaptive site in WP with new themes in my local machine, to later swap the old site. Basically, if I re-install my Google Analytics tracking plugin + FB pixel tracking plugin in the new site, swap it for the old site, go live... what would be the result on the pages that were already ranking high?
Would their rank be reset? There will be nothing new (or text format exchange) in the blog posts, how would this affect my SEO?
Thanks for any tips and suggestions.