How do I keep changes made by the browser console?

Hi, I was seeing the code from some websites on the internet by the console and making some changes to see what happened, and it got to a point where I wanted to save all those changes, even if only for me. (since I know that on the site server this is impossible ...)

The problem is that when I reload the site, it replaces the one I edited with what comes from the server (which makes total sense) but in that way there is no way to know how it would react by loading that document I edited.

That said, let's get down to business:

Is it possible to update a site so that it loads the code I edited instead of what comes from the server?

Is it possible to load javascript documents that I have on my machine directly from the site I'm accessing? (ie a better technique than copying everything and pasting everything into the console)

Thanks for the help and I'm reminded that I just want to make these changes to the site I received and that is in the browser, I know that theoretically everything I said is possible to do (which is one reason not to trust nothing client-side) but I have no idea how.