Hi Suresh, I am assuming that you want to modify premade histones, unless you add a codon for a Cys at a predetermined location. Cys can be specifically modified without cross reactivity with primary amines.
I you want to try it out, isolate histones with DNA attached and treat it with Traut's reagent. Isolated -NH2 groups will have a thiol adduct.
I am not sure if this thread is still open, but should you still be interested have a look at this review: Article Synthetic post-translational modification of histones