I have no idea if Chrome extensions can edit user profile files directly, but my HSTS file is in ~/.config/chromium/[Profile Name]/TransportSecurity. I figured that if not, we could just inject STS headers on the first run (or lazily when someone visits the domain for the first time?) to append domains to that file. We could spoof max-age 0 headers if someone wants to disable a rule.

Seth took a stab at programmatically detecting simple rules in the existing ruleset library that could be recast as HSTS preloads. It didn't work out very well, but definitely worth working on. :/

I used Seth's attempt to make a quick Firefox addon for prototyping adding/removing HSTS rules from the Firefox HSTS db, because you can do that directly in Firefox. You can find it at: https://github.com/diracdeltas/hsts-everywhere