[ixp1200] regarding workbench custom data

Hi, I have some packet data using ethereal.All of it is in hexadecimal.when i cut and paste it in the custom data portion of the data stream all the values change ex the first byte was 50 and it changed to 35 and so on.if i manually change each hexa byte it works but i need to put one whole packet of 1500 bytes (lots of hexa) in the custom data of a particular format .Can anyone tell what i can do instead of having to sit and type manually. Thanks in advance, shweta