I had a quick look at the service manuals (available here) and they state that the ‘Service Tool’ is required to change the region code, so unfortunately you will need to contact a service centre – perhaps ask them to visit you if they have the tool which could be easier than moving the TV.
It is strange that the code has changed, but I think I have read about this problem before on one of the archived forums. The service manuals do also explain how to check (but not change) the current codes.