I have to agree with the others here, the redesign is probably just how they are making the car. Tesla wants to reduce the amount of pieces in their vehicles and make production simpler, faster, and less prone to error.
However that doesn't the Model Y won't change in the near future, and to answer your question about what happens to those who have already gotten their Tesla before the model (any model) gets redesigned, they will just have to deal with it just like with any other company. It sucks to finally have your vehicle delivered, just to find out that they are making some changes right around the corner, but that's a reality. If you want for the changes and then order your vehicle, they'll make more changes. A great example is to look at any other manufacturer such as ford; The F-150 dates back to the 50's and has been changed in some way or another every couple years.
One nice thing about what's coming up in hopefully the near future is that the biggest changes to vehicles could become software related from year to year. That's a big plus about going with Tesla for me, I don't really care if I get my Cybertruck and then learn that next year they're going to make the seat comfier. I do care if I got my Cybertruck and then learn that next year they will release a better full self driving software, but with Tesla, we would all get that whether we bought it last year or next year.