…After a little research, I found two solutions to this problem [of changing a website’s code locally and having those changes persist across browser sessions.]
The first is to use a browser extension. You could make one yourself, but that’s a little too involved for what I’m trying to do, so I turned to an extension called Stylus3. One way to use Stylus is to search https://userstyles.org for the website in question and find a theme you like. Alternatively, you can create new stylesheets right in the browser. You can apply them to specific pages, entire domains, or every site you visit.
The second method is to use web browsers’ native ability to apply custom stylesheets to web pages. In Chrome the feature is called Local Overrides, while in Firefox it’s the Style Editor. In Chrome, you can specify a directory on your filesystem to save the changes you make in dev tools and it will load that stylesheet the next time you visit the site, which is more or less how I think things should work, but for various reasons I don’t use Chrome. Firefox’s system seems to be geared toward developing your own website rather than overriding existing websites, which is cool but doesn’t really work for my use case.”-Dylan, “The Mutable Web.” simulacrum.party. July 23, 2019
Like RSS, this is about taking more control of your experience of content online. Of course, there are styles that can be used to change The New York Times.