The basic problem with this kind of idea has always been that player's would simply take over characters they do not like and then have them commit suicide for no apparent reason or sabotage something in a certain way in order to facilitate the success of a characters that *should* be the enemy of that character. Having the game replace an existing character by having them die for gamey reasons is basically the npc commits suicide for player ends problem actually written explicitly into the mechanics.
Your grammar made that rather difficult to read, but presuming I understand it correctly...
What you're complaining about in the first paragraph is pretty much exactly what already exists in games like Crusader Kings II if you don't play Ironman Mode - you can play as a king of one nation, save, go back to the menu, then start playing as another landed noble. Hypothetically, you can sabotage a nation, then play as a smaller rival to take advantage... But honestly, I've never seen anyone really do that, just because it makes the game dissatisfying.
It is, after all, basically cheating, and if you wanted to cheat, there are more direct ways of doing so. Worrying that players will take advantage of extraneous methods of game manipulation like this is on par with worrying that mods will allow players to make dwarves that do not eat or have emotions.
Aside from that, pretty much everything is already in; we already choose our skills, we also in a very rudimentary way decide our social standing; so I cannot really see how this suggestion is not really already implemented. The only really notable idea on this thread is the potential to define who your (non-historical) parents and other family members are out of the available professions of the site, that would add something to the game but since important people do not have non-historical children being the child of a noble is ruled out.
Most of this thread is basically the player is an omnipotent god that should be able to rewrite history and bend the universe to his will effortlessly. However there is one way that the child of noble wish of the player could be met I can think of. That would be to select an existing historical couple, have them conceive a child that would not otherwise have existed and run the simulation on autopilot for as many years as it takes for them to grow up (or reach a user-defined age). Of course there is the risk that the player's character will come to a sticky end in that time, or end up in a goblin fortress more likely; but that is I guess in the spirit of the game. So in essence the whole concept is kind of "if this couple made a baby now what would happen to it?".
The children of a historical, yes, but not necessarily the grandchildren to the best of my knowledge.
Regardless, there are more important aspects to characters than just their skills. I'd rather see player character personalities modeled. (In fact, I'd like to see player playstyle
actually affect player character personality.)
You may trivialize adding in a backstory to a player character to the point where you apparently don't even acknowledge that
was the main request, but many players would obviously greatly appreciate it.