how can i make ugly sims generate

@Kathrynxz, this might not be what you are looking for, but it might help anyway, so here goes ...

I assume you want some ugly Sims running around your town for either a story or a challenge.  What I would do to achieve that is to make a bunch of households filled with ugly Sims, and then place them in all the empty houses in your town or in your world -- you can even evict preexisting Maxis-made Sims and fill those houses with your ugly Sims.  When you get enough ugly Sim in your town or world (be it 1 ugly Sim or dozens) you can save your game (maybe call it Uglyville if you have a lot of ugly Sims).  Then you can play your main household (I am guessing that this would be a normal looking Sim or family), but many of your neighbors will now be ugly. 🤨 🙂 You never have to actually play as the ugly Sims, unless you want to. 

I realize that this isn't actually forcing the game to make ugly Sims for you, but it is a way to get some ugly Sims as your neighbors in your town. 😃 I don't even know if you can force the game to generate a certain type of Sim.  There might be a cheat, but if there is I never heard of it. 🤔  There also could be a Mod you could use, but Mods can be tricky and can sometimes cause problems in you game 😢 (which is why I don't use them anymore).  That said, there are a lot of creative people making Custom Content (CC) and Mods these days, so it can't hurt to look! 😉

Please tell us if this works or if you find another way to get ugly Sims in your game.  Best of luck & Happy Simming! 🥳