Prevent Sim Generation

The game will assign townies to be in NPC roles because they're not "playable careers." For example, librarian or paparazzi or Realm of Magic Sage or Restaurant Chef/Waitress. If you play the NPC, they'll lose their NPC role and become unemployed.

On the other hand, maybe you really want a Sim you created to be the librarian or a Realm of Magic Sage. That's doable, but you have to mark them unplayed and can never play them (unless there's a mod for that specific NPC role). The following threads might help:

https://answers.ea.com/t5/General-Discussion-Feedback/Replacing-Realm-of-Magic-Sages/m-p/8611471#M20766

https://answers.ea.com/t5/General-Discussion-Feedback/How-to-make-Erwin-Pries-the-Curio-Shop-Owner-again/m-p/10687836#M55444

And for what does and doesn't break NPCs:
https://answers.ea.com/t5/General-Discussion-Feedback/Protecting-NPCs-from-losing-their-jobs/m-p/10700620#M55725

https://answers.ea.com/t5/General-Discussion-Feedback/Cottage-Living-Villagers-Lost-Their-Active-Roles-and-Became/td-p/10556873

There's a whole slew of hidden traits in this thread: https://forums.thesims.com/en_US/discussion/900951/hidden-traits/ I have NOT tried ANY of them.

I've done some things with NPCs like I got Sara Scott pregnant with MCCC so I could fulfill her wish of having kids without "breaking" her, and also have a Sim married to Simeon Silversweater and have never played him, he's our "roommate." Simeon has 3 kids and I used MCCC to check his parenting skill level (he's level 6 from kids asking for help with homework, etc.). So you can marry NPCs (as long as they don't join your household), have children with them, move them in as roommates, etc., but once they're NPCs you can't play them, ever, without breaking them, and some NPCs are fine in houses and others break if MCCC puts them in houses (mail carrier, I hear). You can shift-click to add the Grim Reaper to your household, and an identical one will spawn to do the actual reaping because that's an NPC role.  And yes, another one of my Sims married Morgyn Ember and he retired on his wedding day because I moved him in and played him.

I'm not sure whether that helps or not, but I think that's what you're asking... I hope it does.

Thank you very much for your answer.

Well, my problem is, I want the game to stop generating sims for the NPC roles. I have ~300 households in my save game. I want the game to make use of these. I also have them all set to unplayed and only play with one household. So that leaves ~299 left over. But the game doesn't do it.

At the moment, I can only decide that the game will throw more Sims at me that I don't want in my world or that I will use NoRandom and many places will be empty and unoccupied (e.g. the gym or the wellness centre).

And that is the most frustrating point for me. There are so many mods for this game, but nobody seems to mind that you can only choose between the two extremes mentioned?

@Totuvor 

Edit:

Ohhhhhhhhh, I just reread your initial post, and...

I currently have 199 homeless single households in the "My Households" category and several multi-person households in the "Other Households" category.

Yeah, if they're under "My Households" they're considered "played." Have you tried unclicking the heart to mark them as being other households?

But that sounds really stupid, doesn't it? There is an extra category between played and unplayed with the green crystal and My Households and Other Households. So should I move all the Sims I don't want to play into the Other Households?

Do they keep their careers there if you have assigned them any or are only NPC jobs possible there?

I'll definitely give it a try and hope that this may have been my mistake in trying to understand the game xD

Yeah, if you mark them unplayed they act like regular Maxis townies, like the Goth family who never changes jobs (barring the Neighborhood Stories feature), etc. They age, but they don't get married or promoted or have more kids or move without MCCC story progression, etc.

Unfortunately, your tip didn't help. The game still doesn't take my Sims for the NPC jobs, even though I put them all in other households. The places remain empty.

I'm pretty sure you have to combine that with a mod.

I'm not doing this myself, but Pleasant Sims has a video (called something like "Play the World: How I Play Rotationally") and in it she says that the for-pay version of NPCC works to prevent new townie generation and use HER townies for everything. (I'm using MC Command Center's tray import feature, because my biggest concern is less people in bathing trunks, boots, and a paper bag on their head for every NPC role. This works if you set it to a high percent and have a lot of Sims in your library, but it doesn't preserve households, traits, or skills, which sound like they're important to you.) Since it's for-pay, I really hesitate to recommend it without trying it, but you can probably find her YouTube video from my description. That's not the whole gist of her video, so you might have to skip past the rotational play bit to get to it.

Unfortunately, the trick with MCCC doesn't work either. I deleted all the single Sims from my save again and tagged them all in the gallery with #mccc_include.

As soon as I delete NoRandom, the game creates random sims which are not from my library in the same household around my mccc_include sims, turning them into families. Now you have to imagine: Families should be not tagged so that individual Sims are not torn out of their families. But if you were to do that now, a family father, for example, would be torn out of his family in order to be used for an NPC job and would then get a new wife and child at the same time.

This is so terribly badly programmed.