We don't change a lot of player stats. Only with players who are really underestimated. Like a player who is the biggest talent of Zaragoza but only got -6 as PA. We try not to change a lot of player stats coz most of the times it's just an opinion of someone that a player should be better or worse.
As for updating a player's history... I've made thousands of changes in the editor (perhaps tens of thousands) so it's hard also to update their history accordingly lol.
Hope I've answered all your questions. | 
