Recently Google Chrome has shown local overrides feature in Chrome Canary. Here is the video, the relevant feature starts at minute 4
Here is how to use this feature to change the background color of https://news.ycombinator.com/news for example.
- Open Chrome Canary (I have version 64)
https://news.ycombinator.com/newsand open DevTools
- Open "Sources" tab and then "Overrides" column.
- Check "Enable Network Overrides" and select any folder on the local disk. This folder will keep changes files.
- Click "Allow" when asked to allow Chrome Canary browser to have full access to the new folder
- Select "Sources" - "Network" tab and find the "index.html" document. Edit whatever you want there, for example I changed
<table bgcolor="ping">in the HTML markup.
- Click "Ctrl-S" to save the update file. Notice a purple dot appears next to the file name.
- Reload the page and see the override making the page pink.
Note: in order for local overrides to work, you must have DevTools opened and "Network enabled" which you can quickly trigger from the command palette
On Mac press "Cmd + Shift + p" and start typing part of the command.