Editing Key In a BIN File

My Satellite Setup
Mondeal 9000 Gold
I have a BIN file for my reciever (Mondeal 9000 Gold) that was made for the 19/04/05 AES key change on TPSCrypt. I was wondering how I would go about changing the AES key to the new key changed on the 22/04/05 (N.B. I'm not asking for the key, I already have this).
I've made an attempt at doing this, by opening the BIN file in UltraEdit and replacing the old AES key byte for byte with the new AES key and then saving without making any other changes. The patching software for my reciever sends the file OK and the reciever updates itself but then when I turn it off and then on again (as per the correct procedure) I get a an error message. Is there anything special I'm supposed to be doing. Any help would be much appreciated!

I know there's other threads that cover editing the file itself, but I know how to do that, I just want to know if theres any correct procedure with regards to the AES key, I hope the admins dont mind. :)