You'll get more answers here.
It's OK to do, with a few caveats.
You have to make sure you don't remove a huge percentage, or you could run into problems with the biological filter and you'll be running through another cycle.
Obviously you need to take care not to drop any rocks on your corals or fish, or crush them against the glass.
Sometimes you can have dead zones under the rocks; if this happens, you can release hydrogen sulfide when you move them. In that case, you'll get a whiff of rotten eggs. That's bad. H2S is extremely toxic. For that reason, it's a good idea to have a lot of water ready for a waterchange ahead of time.