No you won't pay the price difference to replace it if faulty.
But if you exchange it for a different item (if faulty), the new price will stand. Or so I found! My speedy B had an issue and had increased in price in the interim. When I exchanged it for the neonoe, they gave me the value of the speedy b on that date. If that makes sense!
Understood! That is very helpful, thank you!