Yes, and you’ll need to do a rebuild. I’m not entirely sure that it’ll downgrade it, though. If not, it’ll be easiest (not to say most expeditious) to copy your
rm -r /var/discourse and rebuild, copying your
app.yml to the new /var/discourse before you bootstrap.
Like @cpradio said, if you’ve got more than a few dozen messages, you’ll want to do an import. It’s not on my shop yet, but I do a no-support quick-and-dirty import for $250. If you need changes to the script, multiple imports or choreographed change over, it costs more.