Putting new/different pads on older rotors is ok to do. 1 thing will happen,
1.- the pads will lose life mating to the grooves of the rotors, by that i mean that the rotors will have groves in them whether visible or not and the pads will not reach maximum stopping power until these grooves are mated to the pads.
It is not a bad thing but not a good thing either.
Change away!