Anybody can tag a topic, this includes you. If you at least put up 4 or 5 tags at the start, perhaps at least 1 will stick.
As to ratings, that's an individual thing, person goes over and clicks the thumb thing in either an up or a down and your thread can be zapped to a 0 or ride high into double (possibly triple) digits. For individual posts, same applies, except a single post can be voted down repeatedly well past the 0. Once it reaches 5 (if I recall correctly) the post itself will collapse from view and will only be seen if an individual clicks on it directly.