So what's the potential to program the security register in an old logger?
I think we need someone with an old data logger to read the Security Register. If it returns anything other than all 0xFF's, then it has already been programmed. If it has, and doesn't match the new logger, this would be a good clue.
But to precisely answer your question, if it has not been programmed previously, it would be a simple task. It could be done with an Arduino, Bus Pirate, etc. If and when the time comes, I'm certain that the full instructions will be published here. If it is already programmed, it cannot be programmed again by any means that I know of.