public CidrBlock setByte(int byteOffset, int n) {
        if (n < 0 || n > 0xFF) throw new IllegalArgumentException("Byte value must be between 0 and 255, but was " + n);
        int byteDiff = n - getByte(byteOffset);
        return addByteRaw(byteOffset, byteDiff);
    }
Set the byte at the given offset to 'n'.  0 refers to the most significant byte of the address.
vespajlib/src/main/java/ai/vespa/net/CidrBlock.java