Seems I was overthinking it; I don't think I really need to read it and write it as Unicode, I just need to read it and write it as bytes. Something like (just to prove the concept):
CODE

$writeTo = FileOpen(".\binary-write.txt", 2);
If $writeTo = -1 Then
MsgBox(0, "Error", "Unable to open file.")
Exit
EndIf

$bin = BinaryString(30);
$bin = Chr(0xff) & Chr(0xfe) & Chr(0xac) & Chr(0x20) & Chr(0x20) & Chr(0) & chr(0x60) & Chr(0x01) & Chr(0x20) & Chr(0x00) & Chr(0x18) & Chr(0x20) & Chr(0x20) & Chr(0x00) & Chr(0x19) & Chr(0x20) & Chr(0x20) & Chr(0x00) & Chr(0xa1) & Chr(0x00) & Chr(0x20) & Chr(0x00) & Chr(0xa2) & Chr(0x00) & Chr(0x20) & Chr(0x00) & Chr(0xa3)
FileWrite($writeTo, $bin)
FileClose($writeTo)