No one wants a cycle, but I don't think you can do anything about it if you do things the way you're going to do them. If you dip your rocks in fresh water you're going to kill all sorts of things, including many of your nitrifying bacteria. I'm also not convinced that the fresh water dip will kill enough of the dinos to make the trouble you'll go through be worth it. You'll kill lots of them, but you'll also kill most of everything else as well. Is the new rock you're going to get already live, or dry rock? Dinos thrive in instability and that sounds like a recipe for instability. Add in a whole bunch of fish that your old dino covered rocks probably don't have the capacity to support right away anymore and you're really just asking for trouble.
If you want to rid yourself of dinos and you think treating the rock is the only way, you're better off being decisive. I'd cycle new rock in the holding tank and move my fish over to it slowly, keeping on top of water quality. Once display is empty, I'd tear it down and start from scratch. Bleach or acid wash the rocks, then cook them for as long as it take for nutrients to stop leaching from them. Then set the tank back up and cycle your guaranteed dino free new rocks as though it's a new system. Then start transferring your fish back over from the holding tank.
However, there are other less drastic ways to deal with dinos, but if you're going as far as breaking down a tank over it, I'd want to be sure it worked.
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