The Aryan clause was a necessity at the time that the will was written. If the estate passed into non-aryan hands there was a very high risk that it would be confiscated by the authorities.
From what I learned about the will (see my last post with the link) there was never an non-aryan clause in it. In it was, alals, the statement that they future bride had to be "nobel" according to the statues of the German Nobility society. And that, at the time the will was written (in war, under Nazi-rule), the statues included the term that no lady with Jewish (or other non-aryan) ancestors could be considered "noble".
That point in the statues of course was removed after the war! And it is true that claiming a bride must be "noble" according to the statues meant she couldn't be a non-aryan.But it is clear from the formulas that the will used which showed how the old prince thought, that there was no Nazi-thinking behind it but that point that in his head there was still a difference between nobles and commoners and he wanted a noble bride for his descendant.
Just like he asked that the bride be protestant, but that in case the protestant church alined with the catholic one, this point had to be removed. So he knew what he wanted, he knew what his time in his country was about, but tried to take care of his wishes for future descendants in a way that there was an organization behind the statues which determined the "noble" birth that could change them when the times changed (as they did for the non-aryan-clause) and that the religious point could be changed/abolished if the times changed in these things as well. But these didn't change.
So he had strict beliefs which are understandable when you think about his life and he had see that it worked in his family before and so he wanted to fix this. But from the will alone you cannot say he was a rascist or a nazi at all.
And nowadays not many people actually care about these statues anymore. Because as soon as one commoner married the holder of a noble name, she and her later kids became "non-noble name wearers", so having one non-noble ancerstor makes the whole bunch of descendants to non-nobles. That was the reason eg. why Francesca Habsburg could not become a dame of the Sternkreuzorden, because not all of her 16 ancestors were of noble-blood.
When we deal with noble inheritances we have to understand that back then (more often than today) rich nobles were the heirs of the successful people during the times of the monarchy and that they wanted to preserve what had served their family well. So they wrote their will asking that for the descendants who wanted a share in the family's riches. In more modern times some nobles changed their views, others stuck to it (just think of the clash in the Saxony-family) but a private estate in Germany is a private thing and there are several possibilities you can use in making your last will and they are all legal. No court will removed them, but, as the analysis of the Berleburg-will showed, no later living descendant can force a court to change the one once stated to more strict ones. Eg. Gustav's uncle claimed that the fact that Gustav and Carina lived together made them legally living in a cohabitation "similar to a legal marriage" and thus Gustav had lost is right to inherit. That's why Carina moved to London, because Gustav and Carina couldn't know how the court would decide, so they were careful to show openly that they didn't even live together at Berleburg!
In the end the Court of law decided that Gustav fulfilled all points required of the next heir, that he was not married and thus he could inherit.
The whole non-aryan and other stuff about Carina being his unfit wife was only brought up by his uncle in the hope Gustav would be disqualified
But the Court made sure that they read the will carefully, figured out what the grandfather had wanted, whether the heir needed to be married (no) and then found in Gustav's favour. All the other legal tricks used to make them reinterpret and sharpen the will were ignored.
A fascinating read for a lawyer interested in inheritance law (and probably a philosopher interested in what greed can make of some people and turn them into obvious manipulators buying experts to help them) but it wasn't a read about a rascist grandfather trying to inflict Nazi-"Values" to his innocent grandson.