This would also be good for the Japanese mod idea if you could adopt members from outside your dynasty (and give them your dynastical name). Although I guess for that I'd prefer it to be as a special edict to allow/disallow so it could work with different existing inheritance laws since according to Doomdark we won't be able to create our own custom inhertiance law.
Good thinking. What I would say is: (1) Doomdark has said that sons can inherit through their mothers and change their dynasty names, so maybe you could change the dynasties of other courtiers to suit your needs; and (2) expect some controversy, unless the adopted son or daughter is already an established member of your realm.