In the current freethinker discourse, agnosticism and atheism are considered to be independent properties - "gnostic" meaning "believing knowledge is possible" and "agnostic" meaning "believing knowledge is impossible". There was a very active agnostic theist poster on the forum then known as the Internet Infidels Discussion Board when I was a regular, for example.

Even if this were not true, changing the definition of the word "atheism" merely means that the word no longer describes the people you are disagreeing with - not that their opinions must correspond to the new word.

(If you are a YouTube fan, QualiaSoup's "Lack of belief in gods" is a pretty good overview.)