MCCC has a setting to select NPC/Townies from your library.Computer/Population settings /Import Tray Settings /100%.
Make sure you have a lot of townies in your Library. I haven’t used this because I didn’t want it applied to every world, so I don’t know how well it works.
I use something similar to your method for The Magic Realm, which, I think, needs 12 Spellcasters available to populate. I have an apartment with 8 in it, and the townies in Copperdale have become Spellcasters. It mostly uses those sims but occasionally still generates randoms, which wind up in unplayed households. I just edit them to make them fit.