Who knows what is canon these days, and what is not? I first heard about the Z-95's back in the old WEG Star Wars days.
I don't think those walkers are AT-ATs. I recently was listening to someone talking about the trailers and they used another term for them (didn't catch it fully). Perhaps, they are a prototype that leads to the AT-AT design.
How have they changed the background of the building of the Death Star? I hadn't really notice too much out of the ordinary. I know they made a few cosmetic changes.