Of course you can. Microsoft's Edge and Brave already add proprietary features like AI and reader mode, tab groups, video calling, crypto wallet etc.
Brave could add a custom CSS or HTML feature. Hell that was the status quo we came from ten years ago when each vendor had their own feature flags and implementation for WebRTC and proprietary video codecs, etc.
Brave already explicitly removes ads and blocks all kinds of things websites expect to work on Chrome.
Nowadays Edge has some superfluous features that differentiate it from Chrome, but they are still superfluous. Underneath it's still Chrome, because the internet demands Chrome.