For the record: it works!
If you upgrade a #Minecraft world to the Village and Pillage update and find that the villages you’ve already explored have suffered complete economic collapse, leaving all your villagers unemployed, you *can* craft the new job site blocks, place them in the village, and watch the villagers rediscover how to do their jobs (and trade with you using the new trading mechanics).
https://hyperborea.org/journal/2019/06/upgrading-a-minecraft-village/