Mrs Waggs pickelig lime paste is excellent at killing aiptasia.
I have changed out pieces of rock in my tanks. The key (as stated above) is to make sure that the new pieces are fully cured, and to only change out a few at a time, and to allow time to the tank to adjust to the change fully ( I have waited at least a month) before changing out additional pieces if desired.
If your not liking the rock b/c of limited scaping options, you can drill/modify it. Just take a rock or 2 out, put it in a bucket of tank water from a water change. Use a masonry drill bit to drill holes that an acrylic rod can be put through so that you can stack the rock higher without the risk of toppling. A hammer and chisel (or dremel tool) can be used to custom fit pieces than can then be held together with reef epoxy and/or acrylic rods. This method IMO/IME gives you the greatest ability to achieve height without the risk of a rock slide or having to lose most of your sandbed to form a stable base for a tall stack of rock. It also lets you create places for coral placement. Flat places made for frag tiles or corals on pieces of LR, and/or holes can be drilled randomly to accept frag plugs too.