I do this all the time, got kinda scared when my hairdressing teacher cut a bit of my hair off, put bleach on it and it turned to chewing gum though .
I find that the best thing to do if you do the black to blond thing is to put hair mayonnaise on and leave it for about an hour. when you rinse it off your hair is in pretty good condition.

well i did it. i no longer have black hair, it's a weird reddish brown and will be for a hot second. but i'm on the road to blonde!