The packet containing the RSA key for bin.pbo contains a hash of made up of your key with another (seemingly) random "authentication" string.
E.g. 0de7ed97545febd23dd38e23d3600e355e4471e3594477f96c03aef8dfdd43d664e911c
The bold part of the hash is based on your key while the non-bold seems to be random each time. Changing the bold part to something that doesn't conform to the algorithm returns "Invalid key" and changing the non-bold returns "Invalid authentication".
When you finally get in the server, a packet is sent beginning with BE containing your GUID. Changing this results in "Client not responding" after about 30 seconds and if you join a server your already banned on, you stay banned. Probably because it also checks the above CD hash.
I guess if you got someone elses CD hash (the bold part), replaced your own with theirs in WPE while leaving the second half untouched so it correctly generates the "authentication" string AND THEN replace your GUID in the BE packet with the one attached to the spoofed CD hash, you could change your "hardcoded" identity. You would also need to send your "heartbeat" packet, as mrmedic calls it, so the server still thinks your BE client is still running correctly.
Just a thought.