Well, as i said in a thread on Steam aswell.
Alternately they could just limit what traits you -can- take and sort it out quite easily. Heck, they can even make it so your created ruler has the original traits of the Original ruler you take over. You just change the gender/appearance/Dynasty/shield.
This would solve the very essence of ''Abusing the Ruler designer'' ( I've no clue how people can do that.

) Keep you to a character of your liking, and still let you get achievements..
I, personally, would prefer this, as i don't much care for traits. Traits is something i get through my actions in game. Not something i allot in the ruler design. I bought the ruler design to -create- a ruler and dynasty i liked. Not to abuse and pack full of traits.
The whole purchase of ruler design for me was that i could, indeed, design my ruler. 'Tis not fun playing as a pre-made ruler face/Dynasty due to all the time i spend looking for a nice ruler/dynasty mark.. And i would like to hunt for achievements with a nice enough leader..
So another possibility for it. Disable the third page on the ruler design during Ironman and just let us change leader and dynsaty and name. ( Granted Dynasty and name is on the last page but it could always be unblocked. )