Default Buying a carrier locked G2 D802

Hi guys, I'm getting a carrier locked G2 (mobiltel Bulgaria) and I was wondering what to expect - are they locking the bootloader and if so - can it be safely unlocked and then brought back to stock if I need warranty repair? Is it possible to unlock the device and use it on different carriers?
Samsung i600 -> T-mobile G1 black -> SGS i9000 -> SGS3 LTE I9305 -> Iphone 5 White-> LG G2 D802 White