I'd argue Funakoshi did, and that's why it's referred to as Shotokan Karate - a specific style of the art.So at what point does changing things make a new style?
Did gogen yamaguchi stop training goju ryu when he made his changes?
Did funakoshi stop training and teaching karate when he made his changes?
Styles of martial arts were constantly changing before the ‘modern era’ so why does changes to style suddenly equate to different styles now?
But that's a valid question, and I don't think there's a clear demarcation. It would depend how uniform the art/style is before the changes. BJJ is pretty open and fluid in its approach. It would take some really major changes for me to look at it and say "that's not BJJ". It would take less change for me to say the same about Judo, I think, and even less for my primary art (Nihon Goshin Aikido). I've even questioned whether what I teach/taught is still the same style as I was taugth because of the changes I've made.