I am a Loner IRL, and I hate social interaction, even in the Sims. I'm a little sick of feeling required to put the Loner trait on every single sim I've ever made. I have S4S, Notepad++ and the most basic knowledge of how modding works. What tuning files would I need to extract, and what in them would I have to change to freeze a motive?

I was curious about your request so went ahead and made it (and basic tested) for you. Turned out to be pretty easy, as I originally thought it might need multiple file changes. For future reference the file you need is:
339BC5BD!00000000!0000000000004112.motive_Social.StatisticTuning

And you just need to set the highlighted text to 0.

I'll keep it updated on my website once it's up.