I have about 130 sims in my game and virtually all of them are of my own design. For service sims, I let the game generate them and then edit those sims in CAS and remove/add traits to taste. You can reduce the amount of generated sims by reducing lots that generate them - each bar needs a couple of barkeeps and some barflys,less bars existing and/or visited then less sims. This allows some control over the size of the game you want to play - stay in one neighborhood with one bar, you will only ever have to edit two barkeeps.
There are a couple of mods/cheats to help. MCCC allows you to simply select any sim in the game and edit just that sim in CAS. After editing, you will simply drop back into your game with your new shiny looking bar person.
Do not alter traits in CAS as the sim can keep a remnant of the removed trait with the odd related negative moodlet popping up - e.g. needs to play video game if the removed trait was Geek.
Traits should be added/removed by turning cheats on and then Shift+click the sim and use the option there to add/remove traits.
Of course, you can use CAS if you want the trait remnant to add a wrinkle to the sim.
MCCC also offers some other population control functions.