For the things like your bta that require stability and high light, I would set up a qt so you can easily control the setup to not stress it out.
Cure the new rock like you stated. When it is time to swap , just take the rock you don't want out. With the water still in, start siphoning out the old sand. This will help with removing as much of it as possible the easy way, just like cleaning gravel in a LFS
freshwater tank. Once it is empty, remove any remaining sand.
Once you switch things over, I would just rip the xenia off the rock and scrub it away with a toothbrush. This way you have more rock to work with for another/bigger project in the future.