Minecraft Zombie Villager discounts?

I know that you get big discounts when you convert a zombie villager back. I would like to convert back the villager with the brewing profession (don't know the name) because 1 rotten meat for 1 emerald appeals to me very much. Now to the question: does the villager have to have the job before I turn him into a zombie or can I give him a new job after the rescue?

As far as I know, profession must already be there

As far as I know, he must already have the job. If you already have a brewing booth, you can just do it that way. So you will be on the safe side.