I use this mod: https://www.patreon.com/posts/assign-npc-jobs-73945932
I use the part that stops random sims from spawning. In order to get the NPC I want at a certain venue, I do the following:
- Get rid of any NPCs currently working there.
- Add my NPC to the game.
- Go into a played household and use the mailbox to give my NPC a role.
- Take a sim from a played household to the specific venue that I want my NPC to work at.
- As long as the game can't create random sims, the NPC I want should show up to work there, during that shift. I avoid going to a venue until I have added and set an NPC for the role there, otherwise you might end up with unemployed sims, like Greg, in the role.
-A lot of venues have 3 shifts and you can do the above during each shift to get the NPC you want.
-Cafe baristas work differently, you can assign them the same way but baristas will show up at any and all cafes and cannot be set for specific cafes. It may work to have several baristas if you have multiple cafes to you don't see the same ones all the time.
I hope this helps.