Blacklisted domains are blacklisted forever, because they crash the crawler. This happens 1x - 3x times per year. Changes here are all tracked and only owners of the first stage of search (who have no connection to the ranking algorithm) have change rights.
Bullet #5: search quality is assessed by thousands of contractors worldwide and you can become a part of the crawl quality team, although it doesn't pay that well in the USA. The book they follow is 180 pages and available on the Google website for many years. It has guidelines for how to determine sexual, offensive, or illegal (or child porn) content in ALL countries. It has guidelines on how to rank news source reputation and credibility.