To choose a sub (to me) is to choose a human being whom you love, adore and respect and to be pleased by the fact that this fine and worthy person is applying the qualities you cherish (and were attracted to in the first place) toward serving you.
If a "Dom" really feels the need to modify the core of his sub's personality, all that tells me is that he never bothered to select someone he appreciated to begin with, and what does that say about how he feels? Not just about his sub, but about himself? *psh* Not my kinda' Dom, sorry...