The plate is a softer material than the castle nut, so you won't damage the castle nut. You may or may not need a new plate, depending on where the notches on the castle nut line up when you screw it back on. That's assuming you want to restake the nut. Some don't bother because it just makes it a pain if you ever want to take it off again.
You need to have an armorer unstake it. There is a HK Staking tool for that. But JNAP probably has another way without using the staking tool.