100: 12 34 56 78 12 34 56 78 A3 ... Interpretation: BCD bytes 12 34 56 78 = 123,456 km. Checksum A3 = XOR of bytes 0x100-0x107.
You want 45,000 km = 0x0000AFC8 hex.
Target: 80,000 km = BCD 80 00 00 00 repeated twice. New bytes: 80 00 00 00 80 00 00 00 . New XOR checksum = 80 XOR 00 XOR 00 XOR 00 XOR 80 XOR 00 XOR 00 XOR 00 = 00 . Write back. eeprom mileage calculator online