If I buy a large quantity of chicken frozen together, can it be thawed, separated, then refrozen safely?
Technically if it was defrosted in safe conditions you could refreeze without too much fear of contamination, but that's not the main issue - quality is. Refreezing meat usually results in a horrible, mushy texture, because of the cell damage caused by freezing. Look for individually vac-wrapped parts if you can find them.
As ElendiTheTall says, the problem here is quality. If you must defrost, separate, then refreeze, defrost the big block as little as possible to pry the necessary pieces apart. You're better off causing some cosmetic trauma pulling partially frozen pieces apart than allowing them to completely defrost and then refreezing.
You can thaw, separate and refrozen the chicken, but from this, the quality of the meat will become worse. Usually, I try to separate the meat before freezing and then take only the piece.