For local testing, add this "component" to your Profiles directory, under lhhcaamjbmbijmjbnnodjaknblkiagon. On MacOS, this is at ~/Library/Application\ Support/BraveSoftware/Brave-Browser-Development/.

lhhcaamjbmbijmjbnnodjaknblkiagon/1/
 |_ manifest.json
 |_ psst.json
 |_ scripts/
    |_ twitter/
        |_ user.js
        |_ policy.js
    |_ linkedin/
        |_ user.js
        |_ policy.js

See psst_rule.cc for the format of psst.json.