Great job, thank you!
Just one thing - it would be great if these rules would not work on strictly moderated instances themselves because there is no point of such highlighting there. We can configure it in userscript setting in UI. But it's better to have such logic right in the scripts itself. So far I have just added this additional condition to the block at the end:
if (isLemmy && !isStrictlyModerated(window.location.hostname)) {
GM_addStyle(...