Amending the Act of Royal Succession - with what results?
Most obviously, the main danger will come from the precedent it sets that Parliaments, both at home and across the Commonwealth, can interfere and amend such arrangements at the drop of a hat, but even more significantly in this particular case on the impact it could have had were it also to be considered retrospectively.
The disputes between the Empress Matilda and Stephen, known as the anarchy, are one such obvious example, but more recently Isabelle of Angoulême, crowned Queen of England, widow of King John and mother of King Henry III among others, had an amazing life and involvement in the disputes between England and France leading to over a century of wars!
An interesting description of her life provides a worthwhile weekend read in pdf format, linked from here or other digital formats from here. It was written by W.C. Jordan and richly referenced, I quote its concluding words on that Lady's life:
No single life, not even one as eventful as Isabelle d'Angoulême's, is an adequate mirror of the social and political events that shaped English and French history in the first half of the thirteenth century. On the other hand, no story of those events can be entirely satisfying — by which I mean morally satisfying — without a great deal of attention being paid to the individual actors who lived through them. It is not always clear what they wanted or why they chose the paths they did to achieve their ends. But the records of joy and anger that accompanied individual successes and failures are precious relics of their moral universe in general ; and in Isabelle's case they reveal a great many of the burdens and terrible dilemmas facing aristocratic women and aristocratic society in the thirteenth century. A pawn herself, Isabelle, it has been suggested, only found emotional satisfaction from making pawns of others ; and yet in the end, her almost disabling resentment of Blanche de Castille and her sons and of the warm relations that bound them together undermines this facile conclusion. We need not end up excusing her moral or emotional lapses (manipulation of children, treachery masquerading as flexibility, failures of self-control, spite) merely because we may in part come to understand the motivations for these actions. Contemporaries, who suffered from them, certainly did not do so. But we may, if we are fortunate,
reach across the chasm of seven centuries and sympathize with the plight of people like herself caught in a maelstrom of intrigue and conventions that seem often to have deflected or extinguished the generous impulses of their characters. One point, in any case, should be clear : the life of Isabelle d'Angoulême is too interesting and too important to be ignored in any serious reconstruction of the aristocratic life or the political history of thirteenthcentury France and England.