It's real important that you do testing for Nitrites, Ph, Ammonia, and you might want to add some stress coat to the water. The rocks are fine. Again I would recommend a good vacuum to keep them as clean as you can. I would not move the rocks either if you're afraid that they'll crush the animals. Test your water once a week, and only add what you need to keep the water stable.
More people kill their fish by adding chemicals.
Also remember that quick changes can cause shock to the fish, so any changes you make should be very gradual. Yes, it's possible that it could spike the ammonia, but I wouldn't make the change until that starts to happen. Monitor it closely, and if you see any changes you'll have to make a decision at that point. It can mix with other fish, one of the real important things though is to make sure the tank is out of direct sunlight or you'll fry your frog. And I would recommend more than one.