YES you can change the number. 1. By reading, modifying and re flashing the EFI firmware. 2. Buy a pre-programed EFI / BIOS (SPI ROM) EEPROM chip for your Mac model (eBay is good) and then replace the chip. These come in 3 different packages depending on what board you have. Once you have replaced the chip you can boot into bank board serializer ans add new serial. 3. Download a copy of BBS (blank board serializer) and make a botable USB stick. Now, many people say that your need to have a gsx account or you can not change the SN if there is already one there but this is pure stuff and nonsense. Fact is, you can use BBS to change the SN as much as you like and anyone with internet access can download it.