Assuming that the inverter is a HF or TL (with built in bluetooth) or has the bluetooth piggy back card installed you should be able to change this with Sunny Explorer running on a PC/Laptop with a bluetooth adapter. I'm pretty sure that you can change this with the installer password (default is 1111) and that you do not need a grid guard code from SMA. However, I can't check at the moment as my inverter has a piggy back card, so you can only connect via Sunny Explorer during daylight hours...