There’s custom moodlets in that sex mod which are like, wearing a strapon so +1 sex appeal, so surely there’d be a way of doing one for being stuffed, for example if weight (or whatever unit that weight slider is measured in on the create a sim screen) goes up x amount in y amount of time give stuffed moodlet, just seems like a simple script.
As for all that amazing stuff, the fact this isn’t a mod for any game ever, nevermind Sims, tells me how hard that’d be lol