If the Floyd was set up properly by a store, it should be proper tension in the strings when you retune it to the tuning which it was. Keep in mind you’ll have to go down the line of strings and tune each about 10 times in consecutive order before they hold the tuning. Each time you tune it will be closer to the intended tuning. You should also reset the height of the knobs on the bridge while you’re doing this. Unlock at the nut and retune with the machines on the head and then when it’s really close, use the knobs on the bridge. Here’s a good video illustrating the process: