Questions: Your Own Sims Filling NPC Roles

You can tag any sims in your library with #mccc_bypass tag and set MCCC so it will pull only sims who are not tagged. Or mccc_include for the opposite.

Also there are settings in MCCC for sim and relationship culling. I can't remember exactly what are they, but I don't have a problem with culling anymore.

You don't need to delete sims from your library!

You do need a computer in game for this: Go to MCCC - MC Population/Population Settings/Import Tray Settings/Import Tray Type and select "Only Other Sims". Then under Import tray percent - set it to 100% and you won't see any more randomly generated sims.

I also select "never use import name" so the game can just randomly generate one. Just a preference because a lot of the downloads have blank last names or something weird. I also leave Import bypass appearance set to default. it will give them random skin tones, hair, and clothing - just another preference because there are quite a few simmers reposting the same sims (not calling anyone out :P) with different hair, eyecolor and clothing and I've downloaded 10 of them before I figure it out and see a bunch of clones walking around in my games :D

To prevent culling: Click the sim in game and select MC Command Center/Sim Flags/MC Command Center/Flag to never cull

Also, you have a much better chance of seeing sims in the world that you put in "not in world" if you give them some skills. For example if you give them at least level 3 dancing and fitness you are more than likely to see them at nightclubs and gyms. You may also want to give them a freelancer career so they don't get stuck working as a bartender for 12 hours a day, which also prevents them from club meetings if it's during their work hours.

Actually putting 8 sims in an empty lot, then giving them flags, skills and a job is the best way to go about it for sims you want to have a good chance of showing up at venues. Then kick them into the void! :D

Awesome! Thanks for the tips and tricks and help!

With mccc if you keep the sims name you can also set it do sims with the same name are never imported at once. Useful because I have multiple copies of my favourite sim. BUT if they marry and change their surname then mccc doesnt recognise them as the same name any more.
I set import from library to about 75% to get some fresh genetics and ideas. But i freeze the appearance of my sims as i dont like their appearance being randomly changed from how I have set it.

Their traits do change though. Not sure if i missed a setting.

1. as far as I know theres no way to designate your own sims as npc in vanilla game the game will keep spawning randomized townies for the roles although sometimes it picks sims in other households if you're lucky and they have suitable skills

2. you can delete households from library it does not affect save itself but if you want those sims safe to be used in other saves or in case of culling or something id suggest you keep copy of tray with all sims in it separate from game

3. so far I've had all my sims in other households and none have been culled or at least ive not noticed such happenings

but ghosts are not safe outside households and without interaction and if you have too many sims it will start culling from the other households or hidden households rather than my households

then again i find it curious because if you never reach max sim count cause your sims are not in my households would the game stil l go culling sims hmn

its a mystery maybe i just don't have so many sims that game needs clearance because i constantly delete my randomized townies as they spawn