The underlying PRINCIPLES of jiu jitsu (and indeed, all combat sports) are as fixed and unyielding as the night sky, rooted as they are, in the unchanging strengths and weaknesses of the mind and physical body of man.
The TECHNIQUES of jiu jitsu, on the other hand, change with the rapidity of the waters of a river, since they are the result of the restless minds of men, who endlessly seek out innovation, change and study in order to gain competitive advantage over each other.
Excellence in jiu jitsu must always involve study of both. Once learned, the principles will provide the unmoving bedrock upon which your understanding of the sport will be based. Technique on the other hand, you will have to continually update and adapt as it evolves around you.