Hi there!
When I started on Webtoons, I had already submitted here a couple of chapters, and I decided to submitt all the chapters on webtoons on one go, to have them at the same than here. I did that because it is way less problem for me to remember in wich chapter I am in what platform, and because there is no reason for one reader to go into the other platform to read ahead, and forget the less advanced one. This was the more viewer friendly solution that I found.
Also, about the remaking of drawings, I don't suggest it, because you lose time to draw new things, and once you finish, you already will have again changed style, and again you will have to start again, and infinite loop!
If you want to tell your viewers that your current style is different, you can always submitt a piece explaining the difference in style, and to ask for patiente until the last chapter. In my case, it happened gradually as I was drawing, so nobody noticed, and only if you look at my last drawed chapter and the first one, you will saw the differences.
At any rate, give it a go at what you think its the best! People will come and read either way!
Good luck!