Welcome to Aquarium Advice! Here you will find some of the nicest and most knowledgable people on the net about fish and their care. Some of them are a little obsessive and anal (ITS TRUE!) but one thing is for sure, you will always get advice that is in the best interest of your fish.
That being said, here is what the gurus will want to know before answering any specific question. Tank size, filtration, # and type of fish, Fish only or reef, and other stuff you wouldnt normally think of posting.
, I think the answer to your question lies in what you really want to do. If you want to resculpt using the new rock, you are best to move the fish to a different tank and go to town. Moving some of the existing sand and live rock is a nice move as you can minimize the new tanks cycling needs. Let the 55 cure and cycle, then add fish back.
If you like what you have and just want to add the new rock, cure it separately and add it after curing. Here is an article on how to cure the rock ( http://www.aquariumadvice.com/showqu...aq=2&fldAuto=6
) that appears in the articles portion of this website.
You will receive opinions from people who have been into this much longer than me, so be patient and get several replies before charging forward.
Welcome aboard, and read read read. You will be surprised what you can find out here.