understand. should be like this. the output bytes still 8 bytes as i wanted. now, i need to do is made the variable byte become something that can be manipulate. how ya?
byte addFingerPrint[] = {0x4D, 0x58, 0x10, 0x03, 0x40}; // 5 bytes
byte variableParts [] = {0x00, 0x00, 0xF8}; // 3 bytes
Serial.write(addFingerPrint, sizeof(addFingerPrint));
Serial.write(variableParts, sizeof(variableParts));