Question

You can do a tint back if you have bleached hair, the only problem is that it can be hard for the hair to hold the color if the hair cuticle is wrecked.

The solution to that is to use a neutral filler, then put permanent black dye on top or a semi permanent toner (choose a neutral base black dye, not an ash dye cause then the hair may turn out grayish)

Think twice before going black, cause there ain't no turnin' back :P It's very hard and damaging to go back to blonde after going black.

I'd actually recommend that you don't go black at all, first of all it will look very very strange to you since you're used to having blonde hair. I'd suggest that you go medium brown or something, before taking it all the way to black.. but it's your hair. Another great tip is to try a black wig to see how black hair works with your skintone and eyecolor etc.