Not only does there exist the possibility of creating your own rules: it's absolutely mandatory. After the Matrix (which only serves to readily generate raw material), you're left asking yourself 'what the hell am I going to do with this?'. The 'teaching' of serial composition is a futile endeavor because as you probably gathered from Wuorinen's text, there really is no point of departure from what you read there (which is already milking Babbitt's techniques as it is). Dodecaphonic serialism isn't the only brand: one could easily work with a smaller pitch space and do other things than what Schoenberg did. It is indeed an older approach to writing music, not one that I have any intention of exploring further for myself, however it's good to have an accurate understanding of an important development in 20th century music.
Curious, how does someone manage to 'disagree' with serialism? I couldn't wrap my head around that one.