Probably, Aagaards Grandmaster preparation series is something like "You must be this tall to enter" while Excelling is more for improving players, although they're still pretty difficult books... His books are kindda difficult to digest, but they are excellent books if you actually read them how you're supposed to... And I don't think the Grandmaster preparation series replace his Excelling at chess series.. I believe that he decided to "dig deeper" into his studies after he got hired by Quality Chess, which in my opinion is one of the best chess publishing companies, if not the best. Besides, Attack and Defense and Thinking Inside the Box are some books in his Grandmaster Preparation Series that have a similar book in his Excelling at Chess series. I'm not 100% certain about all of this, but this are my thoughts as I have read all of this Grandmaster Preparation Series, and most of this Excelling at Chess Series.
Hope my answer was helpful.
Does Aagaard's Grandmaster Preparation series replace his earlier Excelling at Chess series of books?
Is 'Excelling' intended for a lower-level audience?
Thanks