Well of course it won't be a completely new aircraft. And from the 3rd aircraft onwards I expect to come across much more limited design variations resulting in fewer differences in-between prototypes as well as initial production aircraft. The main topic of discussion here is what changes would be considered "fundamental". A drastic change in the eyes of aerodynamicists could be the slight widening of the aft fuselage, whereas for the general audience a drastic change could be the re-positioning of the vertical stabilizers to the side booms or the implementation of a Raptor-like empennage etc. The same goes for people who work on different departments for the MMU program. A slight change for them might end up being drastic for others. This argument can be manipulated and twisted in a variety of ways. There will be changes for sure, but I find it unnecessary to dive into how "drastic" these changes might end up being. Since we are still talking within the compounds of the MMU program, it is only natural for these changes to not be greatly significant. The evolution of Hürkuş is a good enough example to this in my eyes. The most recent (as in it continuously goes through modifications) -B variant flying out there is the most experimental they've been so far. And mind you this comes after CDR. Even so, we can safely regard it as being the same platform with raked wingtips, an altered tailplane and an extended dorsal fin. TAI has gone through many revisions and a bunch of wingtip devices throughout Hürkuş' development but that is out of context. All in all, I believe it is relatively difficult for us to speak of these changes and properly categorize them as such. But changes are a given, and they will happen.