Is there a way to edit online websites locally and keep a copy of only the edited files, so when I visit the page next time, those copies get replaced with the original ones coming from the server. You can do this with Google Chrome Developer Tools but those changes get lost when you refresh the page accidentally or intentionally. Because of this Inspect Element is good only for temporary changes.
Switcheroo is a nice little chrome extension that redirects addresses to other ones.
To use it for your purposes you would:
1. Edit the page 2. Press Ctrl-S and save the edited page somewhere 3. Set up Switcheroo to redirect the original url to `file://path/to/saved/file`
file:// protocol allows you to browse files stored on your computer.