The big problem with copper and live rock is that the copper gets absorbed by the live rock and will leach it back into the system, slowly over a long period of time. This just about ruins it for use in a reef tank. It will prevent most coral related livestock from growing on it.
With hyposalinity, you'll kill most of the live material on the live rock. This can cause a massive ammonia spike. However, at least the rock can still host new growth.
Treatment using hyposalinity usually reduces SG, slowly over several days, from a normal 1.025 to about 1.012, and holding it there for about 4 weeks.
This is why it's best to always treat in a quarantine tank.