Several false things here...
1) The dynastic laws in France have not been established once, but little by litte, since Hugues Capet, not before. Every time the preexistent laws are insufficient to determine the right king, another laws is established inside this corpus. As it is a convention, if not a faith, that there is a laws we discover little by little, new laws must not be in contradiction with past accessions.
2) Many kings and jurists said and wrote they could not change the order of succession, this includes Louis XIV, Louis XV : "puisque les lois fondamentales de notre royaume nous mettent dans une heureuse impuissance d'aliéner le domaine de notre couronne, nous faisons gloire de reconnoître qu'il nous est encore moins libre de disposer de notre couronne même" and Louis XVIII : "Le droit divin est une conséquence du dogme religieux, de la loi du pays. C'est par cette loi que, depuis huit siècles, la monarchie est héréditaire dans ma famille. Sans cette loi, je ne suis qu'un vieillard infirme, longtmps proscrit, réduit à mendier un asile; mais, par ce droit, le proscrit est roi de France".
3) As far as I know, neither Eudes, nor Robert, Robertians (i.e. ancestors of Capetians), sent anybody to convent nor usurpated the throne. First, they had interbred a lot with Carolingians, and were close parents. Second, Charles the Fat, Carolingian, was dismissed because of his behaviour in front of the Viking invasion, and Eudes was elected instead, because of his heroïc attitude. When Eudes died, his brother Robert refused the crown, and supported Charles the Simple, son of Charles the Fat, but this last king became tyrannic and the nobility revolted, electing Robert I who, this time, accepted. At Robert I's death, his son, Hugues the Great, refused the crown; as the nobility refused to restore Charles the Simple, they elected Raoul of Burgundy, a Niebelungen(?). At Raoul's death, Hugues the Great refused the crown and installed on the throne, Louis IV, son of Charles the Simple. Louis IV had two sons : Lothar and Charles of Lotharingia. Charles left Lothar to ally with their ennemy, Otto II of Germany, and fought against his brother and all the nobility. At Lothar's death, his son Louis V (his father had already crowned him, to avoid elections) became king, but died young, childless. The nobility refused to elect Charles of Lotharingia, in war against them, and elected Hugues the Great's son, Hugues Capet.
4) The customs you cited, neither are obscure, nor were altered. They were completed when necessary, but never altered. The fact is that, by the time of the first Capetians, the very concept of Capetian royalty was uncertain!
5) About God's intervention, it is a matter of faith. One may consider this laws was made, and protected, by God; others can consider it was made by men and protected by God (intervention of St Joan of Arc); other may consider that it was simply made by men, but it is an existing laws, thing highly appreciable at the time of electing a king, letting men picking among candidates always leading to troubles. I note that any idea of an intervention of God upsets you, and meanwhile, your opinion is not the third way.
6) The dynastic laws was supposed to be oral before French Revolution, but in fact, were written and commented so many times... particularly, Louis XIV repeated them in his testament...
7) Of course, Philippe V constituted the royal house of Spain, so what?
About Utrecht renouciation, I think I proved clearly enough they were not valid.
8) It is a fact that the current order of succession to French crown is :
1/ Louis de Bourbon, duke of Anjou
2/ Juan-Carlos, king of Spain;
3/ Philip, his son, prince of Asturias;
4/ Francisco de Borbón y Escasany, duke of Sevilla;
5/ Francisco de Borbón y Hardenberg, his son
etc
I am absolutely not sure that the king Juan-Carlos would be pleased to become de jure king of France; it would create him many real problems on his real Spanish throne, for a very hypothetic French throne. But what he wants is one thing, what he is is another.