Yes, yes, yes, to all of this. I might be letting my inner control freak show here, but I've put so many hours into creating and subsequently cheating my NPC sims in new saves before the game even has a chance to generate sims for the roles (usually relatives of other sims so they're less likely to be culled or have their relationships culled). It's satisfying seeing them around doing their jobs, but I'd LOVE an easier, quicker way of making my own NPCs (and not having them immediately lose their jobs upon becoming playable).
As for mods, there is Paulson's NPC Control (NPCC), which reduces the rate at which some NPCs generate and uses your own sims to fill those roles instead, while also adding a new menu to allow you to manually assign NPC jobs to sims (they still have to be unplayable though, and in the case of Strangerville NPCs, must either live in Strangerville or be homeless).
It does make the process a lot easier but has it's own issues, among them being that some positions (like bartender, gym trainer and unfortunately librarian) are location dependent and can be finicky because of this. For example, if you want a gym trainer to work at the gym at San Myshuno, you have to go their with a playable sim and bring the other sim with you and assign the job to them at that lot, and they will only work at that lot, with them losing their job if you bulldoze or replace it, or change the lot type. Also, a sim being assigned as a librarian (either randomly through gameplay or you doing it manually) will result in their traits being replaced with bookworm and neat and nothing else (even if two of their traits were already bookworm and neat), as librarians apparently must have both of these traits. Cheating the third trait is easy enough, if a bit annoying. For this reason, I tend to not have the mod active and only put it back in my game when I need it. Still, it is useful!
