In my opinion it should be possible to paste a hex string (e.g. 05af 12be 323f) into the hex box. This should be recognized as a hex string and interpreted as such, not just taking the ASCII values of the characters.
I wrote some code to do this, it basically tries to parse a string as a hex string and if it fails, it inserts it as normal data (the "old" behaviour).
I only changed the Paste() method a little bit and added a TryConvertHexStringToByteArray(string) method.
Have a look, and do whatever with it, if you like it.
Otherwise, it's a nice control you did!