It'll take awhile to get a build up of beneficial bacteria in the rock pores but it'll eventually all turn live. Buying a "live rock" and adding it will have no real effect on turning the other rock "live" in my opinion. The live rock added will help aid in cycling a little bit, but that is where I've just used Dr. Tims live bacteria to kickstart the nitrogen cycle. I've always used dry rock just because I am paranoid about all of the possible hitch hikers involved in live rock.