This firefox addon can spoof useragents:https://add0n.com/useragent-switcher.html

You're going to need a special hat.

Ever heard of https://12ft.io/ ? It allows you to bypass alot of pay walls by basically pretending to be a search engine trying to index a website. For SEO reasons a lot of pay walled sites allow search engines to access the whole article to index. 12ft.io leverages this to show you whole articles behind paywalls. This is something you could also achieve by spoofing the User-Agent. It would probably work for things like Pinterest without an account as well, but that's something I have never tried (since I have no interest in the cancer that is Pinterest).