I'm building up the new site at habitablezone.net to avoid interrupting service. When it's all ready, I'll decommission this version of habitablezone.com, and then switch habitablezone.com to display the new site. Both addresses will point to the same place. (Unless I'm convince to reverse my reversal of the idea of splitting into two sites.)

So the change amounts to changing over the software. Initially it'll be like amnesia, with no historical posts. But ASAP I'll write some software to convert the old messages from the old format to the new format, and our communal memory will be restored.

I hadn't thought about preserving old-format URLs, but it should be possible. I'll be recording the old ID numbers when copying over the messages, but each message will get a new primary ID # under the new system. Having the old number also around makes it possible to do a lookup from the old number to the new. Just thinking aloud; the short answer is "I'll take care of it".