I think with the lyric "I need a change. Not to imitate. But to irritate" could be to do with the fact that when Silverchair started out, some people said they were nothing but Pearl Jam or Nirvana rip-offs, hence the 'immitation'. Then when they change their style, people will realise that they aren't rip-offs and therefore be 'irritated' by the fact that they were wrong.
I think with the lyric "I need a change. Not to imitate. But to irritate" could be to do with the fact that when Silverchair started out, some people said they were nothing but Pearl Jam or Nirvana rip-offs, hence the 'immitation'. Then when they change their style, people will realise that they aren't rip-offs and therefore be 'irritated' by the fact that they were wrong.