I don't know the exact ins and oust but it seems that a lot of other things have changed not just the constitution referring to the Grand Duke and monarchy. It seems like, as you can imagine given the old constitution was 175 years old, it didn't reflect modern Luxembourg. One example - the annual allowance for the Grand Duke and heir were set out in the old Luxembourg Franc currency - no longer used and replaced by the Euro. It looks to me like its been in large part a "cleaning up" to allow the constitution to reflect the Grand Duchy of today. Most of the changes regarding the monarchy seem to have already been in place (change to succession laws etc).