I know it was awhile ago, but: I think there is a hard-coded limit to the number of separate Professions that are available. Mods like Colonial Charter, and others, make full use of all that they can and they still have to double-up on Professions for types of Work.

That being said, if you're not using other mods and only wanted "this one thing that created Orchards tended by Orcharders" then... It could probably be done and you, yourself, might be able to do it if nobody else will. (AFAIK, modding for Banished is fairly easy as there's not a whole lot of mechanics exposed that you'd have to fiddle with.)

https://banishedinfo.com/mods/resources/gettingstarted

Check out the "A Building and Profession" example.

I think it comes from the way the game has some shared code between farms and orchards (Drag-to-size "buildings", with a pick of what to plant, based on "seeds" you have available), and one thing they share is the type of worker.

You can create new buildings and assign an existing type of worker to them (creating a tin mine and picking the game's default miner as job for example), but I don't think you could go and tell the game that Orchards are not "different fields" and require a different type of worker. By default they're the same thign and share the same pool of workers.

I suspect that to have "Orcharders" as a different job, mods would have to create a different kind of Orchard, of set footprints, and producing fruits out of thin air or requiring a random input (fruits, fertilizer), independently of the seeds you get from a merchant. That's basically what some "Greenhouses" do.