The Radio Code as you call it on Peugeot Radios such as the RD4 is actually the VIN code for the vehicle it is installed. Once the VIN code has been entered in to the Radio (using the Peugeot DIAGBOX software / Lexia Interface) it will not need to be entered again unless the Radio is moved to a different vehicle.
So even if your car suffers a power loss or you disconnect the battery the Radio will still work !! Unlike some other cars where you have to enter the Radio code every time the battery is disconnected to get it working again.
I hope this answers your question and you don't need to worry about any Radio codes.