Hi,
Due to hardware and localization reasons, users cannot switch between A and G versions. Normally if you tried to flash A version on global devices, it will remind you 'Firmware corrupt' and you can reboot the phone and get back to your original firmware. If you tried to flash versions with illegal ways, the phone might be bricked, and your data security will be compromised. Also by flashing different versions, the warranty will break and you cannot enjoy after sales services.
Thanks