I really like the idea, I'm less enthused about the account tie-in, even though I do get why it exists. I'm not sure off the top of my head what a better solution would even be. It is good that you can still manually maintain your own filters if you want and just copy the rules in, so there's value here even for people who don't want to make accounts.
And I do really like the effort to make this kind of stuff more accessible, I think it's understated how important it is to have a nice a site with a tutorial saying "here's how you add a filter", and that there's a ton of value in making it easier for normal people to update that. I'm happy to see people helping to meet that need.
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I'll look into possibly making a pull request when I have more time, but for whatever it's worth, here are my HN rules that hide my own karma from me without otherwise messing with any of the site's formatting. I've found that making my own karma invisible helps me avoid some of HN's more toxic qualities:
news.ycombinator.com##.comhead .score:style(overflow: hidden; display: inline-block; line-height: 0.1em; width: 0; margin-left: -1.9em;)
news.ycombinator.com##.comhead:not(.sitebit):style(overflow:hidden; display: inline-block);
news.ycombinator.com###hnmain > tbody > tr:first-of-type table td:last-of-type .pagetop:style(font-size: 0!important; color: transparent!important;)
news.ycombinator.com###hnmain > tbody > tr:first-of-type table td:last-of-type .pagetop > *:style(font-size: 10pt; line-height: 1.45em;)
news.ycombinator.com###logout::before:style(content: "|"; padding: 0.25em;)
news.ycombinator.com##form.profileform tbody tr:nth-child(3)
HN is pretty annoying to customize because the generated HTML is so bad, but the site is also really static, so filters almost never need to be updated. I've got a couple more janky ones that I use for blocklisting certain users or filtering articles, but they're not really reliable or consistent enough for me to share imo.
Caveats: I haven't tested these on mobile because I tend to avoid HN on mobile anyway, but I probably should test them sometime to make sure they don't break anything there. Also, some of these rules won't completely hide the elements from screen readers. It won't break anything, it just won't get rid of every reference to your karma. Unfortunately because of how HN's HTML is set up, it's kind of tricky to do better, but maybe I can try to think of something later that works better.