The NBA's anti-zone rule is definitely an artificial rule by joev's definition, particularly since it applies only within the realm of that league itself, and really contradicts the way the game is played in every other setting.

Conversely, I wouldn't consider American football's receiver-eligibility rules artificial, since they apply at every level of organized play (and even apply, with certain modifications, in two variants of the game, Canadian football and arena football). Closer to joev's definition would be the NHL's decision as of the 1999-2000 season to use 4-on-4 play during the five-minute overtime period in the regular season.