From my understanding the reason you get this warning is because you need to read and modify the sites a user is visiting, via a content script.

Your manifest.json likely has something like this:

"content_scripts": [{ "matches": ["<all_urls>"], "js": ["content.js"] }]

If you change <all_urls> to https://reddit.com the warning should change from all websites you visit to just reddit.com I believe.

I have an extension doing something similar. Just an fyi, if you want to make requests to another domain you can do this via a background script as well, as described on stack overflow. With this you do not need to request permissions in your manifest. For instance, my permissions just looks like this:

"permissions": ["storage"]

and I make cross domain requests from my content script. This won't change the "read and modify" warning, but just wanted to add this.