Well it did change things for Amelie and Liam. Because until the birth of their cousin Charles it was his older sister and not young Liam who was the first of their generation in line of succession after their uncle Guillaume and father Felix. If for some reason little Charles grows up to find that he is unwilling to succeed it will be the current Grand Duke's granddaughter who will succeed after her father (all under the scenario Charles remains an only child and im expecting he won't be).
Does this answer my question about the second daughter of the original duke of Marlborough? That she, too, would have inherited the dukedom in her own right, had she survived her older sister?
As noted, such a succession would have been akin to the 1907 Nassau Family Statute, which made the six daughters of Grand Duke Guillaume IV of Luxembourg into equal agnates. Female inheritance would be permitted only for their generation, but restricted to male lines in the future.
Of course, Parliament amended the constitution in 2011 to change the succession law to fully cognatic, but effective only with the descendants of the present sovereign, Grand Duke Henri. So his niece and sisters and excluded.
Not that they would have any chance of succeeding, anyway: in today's world, unless one is the heir, he doesn't really stand any chance of sitting on a throne. So the fact that Princess Alexandra displaced her younger brother, Prince Sebastian, has turned out to be irrelevant, since her oldest brother, Hereditary Grand Duke Guillaume, finally got an heir.
Yes, she would. Letters Patent of 1900 allowed the dukedom to be inherited by daughters of Princess Louise but excluded female inheritance in further generations