Villagers permanently keep profession

1 – Get some villagers

2 – Put down some workstations (in this case lecterns)

3 – Watch as villagers become librarians

4 – Check out their trades (BUT DO NOT TRADE WITH THEM)

4 – Break lecterns

5 – Wait for villagers to loose their profession

6 – Wait

7 – Wait

8 – Wait

9 – Wait

10 – Wait

11 – Give up and play something else