Interesting quote from Da Vinci. Especially considering that he was such a stickler to the rules in his paintings. In fact, I was told by an Art professor that Da Vinci, in his opinion, was the perfect example of classic compositional rules.
I just reread the quote. Are you sure he wasn't saying: If you paint only by the rules you have not accomplished anything.
I am not sure if he is releiving the readers of the encumberance of knowledge. I think he is was saying that for the knowledge to be useful that it must be used in conjunction with intuition. This of course is only based on the little that you have provided and a quick search on the net.
I know the rules to play piano. I can read the music and play the notes but that is not enough. It is pure. All feeling is removed. The emotion is not there. I know that a D# is a D# and the next note is an A flat but that is nothing without the intuition to fill those two notes with life. Inversely I cannot just intuitivly start pounding on the piano and make music. I have to have prior knowledge of the workings of a piano and even what a piano is before I can make it "come to life". There are of course exceptions, but they are an extreme rarity.
Is there a non-old-english translation of this book. I gave up old english in college. To damned mind numbing. I lose the meaning of the words as I try to pronounce the words.
the quote hints at a purpose beyond the rules but in no way says the rules are not essential.
Hope this makes sense.